Topic hub — 2026-10-23
Does the bitterness of wine change with contact with the skins and seeds (skin maceration, extraction time, fermentation on the skins)?
To be clear from the start, this page is about studies that, for the same grapes (or the same model wine liquid), changed only the days or the method of contact with the skins and seeds and looked at how bitter people found the result. It is not advice on making or drinking wine. Astringency is treated separately from bitterness. Wine that tastes bitter is sometimes said to taste so because it stayed in contact with the skins and seeds for longer. So what do studies say that changed only the conditions of contact for the same grapes and had people rate bitterness? This page lines up the included studies, study by study, together with their conditions: the kind of wine, the method of contact, and who rated it on what scale. To be honest at the outset, within what could be obtained, not much has been measured. Among studies that had people rate bitterness while comparing conditions of contact, this page mainly covers eight, and only four of them published values for each condition. Of the other four, three mainly give a sentence reporting that no difference in bitterness was shown, with no values for each group or values in a figure only, and the remaining one does not show an individual test result for bitterness. In addition, contact comparisons put on hold because values or tests could not be checked, and studies read in the abstract only, are also in the table. Among those with values and a test, only one study compared fermentation on the skins for the whole fermentation with a control in white wine. One report whose direction reads the other way was put on hold. Five sources that could not be obtained from the publisher's page or elsewhere, so that values and tests were not checked, are in the table of what was searched. Among the included studies, comparisons with long contact during or after fermentation had higher bitterness scores in some, comparisons with short contact before fermentation showed no significant difference in others, and removing the seeds lowered scores in one. For this reason no overall direction is stated, and each study is described on its own. Some studies show values only in figures, give no test result for the comparison, or were read in the abstract only, so please check the test in each row. Grapes, scales, raters and aggregation differ by study, so values are not compared across studies or turned into ratios. This page then separates what was established within one experiment, what differences between studies might explain, and what this comparison alone cannot separate. How bitterness, astringency and egumi differ and how they are recorded is covered on the page Bitterness, Astringency, and Egumi.
On this page (10 sections)
- What this page establishes
- What the included studies allow us to say
- Bitterness ratings at a glance
- Conditions and results, study by study
- What was established within an experiment
- Candidate explanations for the differences
- What is not known — what this comparison alone cannot separate
- How studies and rows were counted
- What we looked at
- Read in the encyclopedia
What this page establishes
- That this page lines up, study by study, studies in which people rated bitterness while only the length or method of contact with skins and seeds was changed; that of the eight mainly covered, four published values for each condition, and that the others are reports with only a sentence about the test result, reports without an individual result for bitterness, abstract-only reports, or values that are only in figures or supplementary tables.
- That there are studies in which bitterness scores rose in comparisons with long contact during or after fermentation, and studies in which no significant difference was shown for short contact before fermentation, and that removing the seeds lowered scores; that the direction is described study by study and no summary statement is made.
- That, among those with values and a test, one study compared fermentation on the skins for the whole fermentation in white wine, and that there pH, acidity and sugar also differed besides the skins; that in fermenting wine the days of contact and alcohol move together.
- That there is one report whose direction reads the other way, and that it was put on hold because, for example, there is no test; and that a report crossing pomace contact with another treatment, so that the direction for pomace contact alone cannot be read, was also put on hold.
- That rows from the same study are not independent, that the scale differs by study so values are not compared between studies, that bitterness and astringency are separate items that do not always move in the same direction, and that no significant difference does not mean there is no difference.
What the included studies allow us to say
- Among studies that had people rate bitterness and compared conditions of contact with the skins and seeds, this page mainly covers eight (Lisjak 2020, Aleixandre-Tudo 2015, Pazos 2026, Jagatić Korenika 2023, Orbanić 2023, Blackford 2026, Magrini 2016 and Stoffel 2025). Only the first four of them published values for each condition. Three, Orbanić 2023, Blackford 2026 and Magrini 2016, mainly give a sentence reporting that no difference in bitterness was shown, with no values for each group or values in a figure only (for Orbanić 2023 the figure was not obtained, so values are unconfirmed). Stoffel 2025 gives no individual test result for bitterness and is treated as having no result reported. In addition, the table has contact comparisons put on hold because values or tests could not be checked (Iino 2004, Sancho-Galán 2021, Philipp 2024 and Yuan 2025) and a study whose abstract only was read (Sokolowsky 2015). Among white wines, fermentation on the skins for the whole fermentation was compared with a control in only one study among those with values and a test, Aleixandre-Tudo 2015. Because the kind of wine, the method of contact and the scale differ by study, no overall direction is stated, and each study is described on its own. [rows: Lisjak 2020 Seed extract in the model wine liquid: 3 days vs 20 days of extraction; Aleixandre-Tudo 2015 Fermentation on the skins for the whole fermentation: control vs FoS [other differences besides the skins]; Pazos 2026 Maceration: control (10 days on the skins) vs extended (8 months) [main effect]; Jagatić Korenika 2023 Plavac mali 2014 vintage: maceration of 7 days vs 49 days; Orbanić 2023 Teran (red): standard 7 days vs 5 treatments with a 48-hour pre-treatment and extended maceration (15 or 30 days in total) [values per treatment in a figure only]; Blackford 2026 Divona (white): direct pressing vs 12 hours of pre-fermentation maceration at 12 °C [no mean per group, no technical replicates]; Magrini 2016 Sangiovese (red): standard fermentation vs cold soak for 48 hours or cryomaceration [no values]; Stoffel 2025 Syrah (red): reference (punch down, not chaptalised) vs extended maceration (rated at 3 months) [no individual result for bitterness; answers relative to a reference]; Iino 2004 Koshu (white): fermentation as juice vs skin-contact fermentation (3 days at 25 °C or 5 days at 15 °C) [yes or no only, no numbers of people, 5 people, no test; no direction label (no numbers)]; Sancho-Galán 2021 Palomino Fino (white): skins added during fermentation at 0% vs 100% [values in a figure only; no direction label (values not checked); no test result for bitterness in this pair]; Philipp 2024 Grüner Veltliner (white): direct pressing vs fermentation on the skins [no test, 1 pooled CATA sample; no direction label (numbers of mentions not obtained)]; Yuan 2025 Merlot (red): stored without pomace vs stored with prolonged pomace contact [the direction for pomace contact alone cannot be read; crossed with microwave treatment; no test; values in a figure only]; Sokolowsky 2015 Riesling and Gewürztraminer (white): wines made with different skin contact times [abstract only, no values; no direction label (no values)]]
- The comparisons in which bitterness was shown by a test to rise differ in conditions from study to study. In Lisjak 2020, 20 days of extraction of seeds in the model wine liquid was higher than 3 days (rank sums 27 against 11), and day 15 of fermenting Cabernet was higher than day 3 (30 against 7; ethanol also rises at the same time). In Aleixandre-Tudo 2015, Chenin Blanc fermented on the skins for the whole fermentation was higher than the control (46.70 against 30.36; pH, total acidity and fructose also differ at the same time). In Pazos 2026, 8 months of extended maceration was higher than 10 days on the skins (46.83 against 37.61). In Jagatić Korenika 2023, 49 days of maceration of Plavac mali was higher than 7 days, 4.81 against 4.23 in the 2014 vintage and 3.61 against 3.54 in the 2015 vintage (the difference in the 2015 vintage is small). [rows: Lisjak 2020 Seed extract in the model wine liquid: 3 days vs 20 days of extraction; Lisjak 2020 Wine during fermentation: day 3 vs day 15 [ethanol also rises with fermentation]; Aleixandre-Tudo 2015 Fermentation on the skins for the whole fermentation: control vs FoS [other differences besides the skins]; Pazos 2026 Maceration: control (10 days on the skins) vs extended (8 months) [main effect]; Jagatić Korenika 2023 Plavac mali 2014 vintage: maceration of 7 days vs 49 days; Jagatić Korenika 2023 Plavac mali 2015 vintage: maceration of 7 days vs 49 days [the difference is a small 0.07]]
- No difference in bitterness was shown for short contact before fermentation. The 12-hour skin contact at 4 °C in Aleixandre-Tudo 2015 had the same letter as the control (31.16 against 30.36), and the 12-hour pre-fermentation maceration at 12 °C in Blackford 2026 gave p=0.912 (the authors write that the lack of technical replicates limits statistical power). For the cold soak of 48 hours and the cryomaceration in Magrini 2016, the text says bitterness was not significantly affected by any factor, but no values are shown. Not showing a significant difference does not mean there is no difference. [rows: Aleixandre-Tudo 2015 Contact with the skins before fermentation (4 °C, 12 hours): control vs ScBF; Blackford 2026 Divona (white): direct pressing vs 12 hours of pre-fermentation maceration at 12 °C [no mean per group, no technical replicates]; Magrini 2016 Sangiovese (red): standard fermentation vs cold soak for 48 hours or cryomaceration [no values]]
- Some comparisons that include long contact also showed no difference. For Teran in Orbanić 2023 (standard 7 days against treatments with a 48-hour pre-treatment followed by 13 or 28 days from the start of fermentation and maceration to the end of extended maceration, 15 or 30 days in total), bitterness is described as statistically equal across all treatments (the source's wording); the range over all 6 treatments is 3.86–4.45, but the values per treatment are in a figure only, and the figure was not obtained, so values are unconfirmed. For Plavac mali, 21 days also showed no difference from 7 days (4.33 against 4.23 in the 2014 vintage and 3.57 against 3.54 in the 2015 vintage; Jagatić Korenika 2023). For Syrah in Stoffel 2025 (extended maceration, rated at 3 months), the text says the only taste or mouthfeel attribute significant by Fisher's exact test was the astringency sub-quality "satin", but the numbers of bitterness answers and the test result are not shown, so it is not counted among studies that showed no difference. [rows: Orbanić 2023 Teran (red): standard 7 days vs 5 treatments with a 48-hour pre-treatment and extended maceration (15 or 30 days in total) [values per treatment in a figure only]; Stoffel 2025 Syrah (red): reference (punch down, not chaptalised) vs extended maceration (rated at 3 months) [no individual result for bitterness; answers relative to a reference]; Jagatić Korenika 2023 Plavac mali 2014 vintage: maceration of 7 days vs 21 days; Jagatić Korenika 2023 Plavac mali 2015 vintage: maceration of 7 days vs 21 days]
- Bitterness scores fell when the seeds were removed. In Plavac mali (Jagatić Korenika 2023) at 49 days, going from seeds kept to seeds removed, scores fell from 4.81 to 3.56 in the 2014 vintage and from 3.61 to 3.49 in the 2015 vintage, and the direction was the same at 21 days (from 4.33 to 3.71 in the 2014 vintage). This compares the presence of seeds, not the length of contact, and is described as a finding separate from the rise in bitterness with longer contact. [rows: Jagatić Korenika 2023 Seed removal: Plavac mali 2014 vintage: 49 days vs 49 days with seeds removed; Jagatić Korenika 2023 Seed removal: Plavac mali 2015 vintage: 49 days vs 49 days with seeds removed; Jagatić Korenika 2023 Seed removal: Plavac mali 2014 vintage: 21 days vs 21 days with seeds removed]
- One report reads in the other direction from its text and table entry and was put on hold (there are no numbers, so the table gives it no direction label). In Iino 2004, a bitter aftertaste is written in the taste column of Table 2 for Koshu white wine from juice fermentation and not for skin-contact fermentation, but the rating was only whether 5 expert panellists pointed it out, with no numbers of people and no test, and in the pair at 25 °C alcohol also differs (9.8% for M-25 of skin-contact fermentation and 11.6% for J-25 of juice fermentation; both are 10.6% in the pair at 15 °C). The Merlot in Yuan 2025 comes from a design crossing the presence of pomace with microwave treatment; in the sensory paragraph the subject that lowered bitterness is the microwave treatment, and the direction when only pomace contact changes at the same microwave condition cannot be read. There is no test of the sensory results, and the values are in a figure only, which was not obtained, so values are unconfirmed. [rows: Iino 2004 Koshu (white): fermentation as juice vs skin-contact fermentation (3 days at 25 °C or 5 days at 15 °C) [yes or no only, no numbers of people, 5 people, no test; no direction label (no numbers)]; Yuan 2025 Merlot (red): stored without pomace vs stored with prolonged pomace contact [the direction for pomace contact alone cannot be read; crossed with microwave treatment; no test; values in a figure only]]
Bitterness ratings at a glance
Human bitterness ratings only. Grapes, scales and aggregation differ by study, so values are not compared across studies. The two conditions compared are set out in the label with the reference (no or short contact, seeds kept, low alcohol) before "vs" and the condition compared (longer contact, fermentation on the skins, seeds removed, high alcohol) after it. In rows about removing seeds, the seeds-kept condition comes first and the seeds-removed condition second. The "Direction" column shows which condition was more bitter ("... more bitter"). Rows that are not intensity scores, such as numbers of people pointing out bitterness or numbers of mentions of bitterness, show "... higher". The direction is shown only from which published value is larger. Rows without values, or whose values are only in figures or supplementary tables and were not checked, get no direction label (they show "Direction not given"), and the direction stated in the text or abstract is given in the note under the row in the detailed table for each study. The direction is not necessarily the result of an individual test between the two conditions shown. Whether the difference is significant is shown by the test in the same "Direction / test" column; even in rows with no significant difference, the direction shows which value is larger. Rows with no test result shown are not described as not significant. Rows with only test marks for each sample, and no result of a test of the pair of conditions shown, are labelled "no result reported". Rows whose values are only in figures we did not obtain are marked as such, and for rows where only a rough visual reading of a figure exists, no number is given. A tag at the start of each label shows the kind of axis compared: no tag for the length or method of contact with skins and seeds; "Seed removal" for removing only the seeds at the same number of days; "Alcohol (not a contact variable)" for varying alcohol or ethanol; and "Substance threshold (ethanol solution)" for tests of a substance in ethanol solutions, which are not wine. The square brackets at the end of a label give the main caveat for reading that row. Select a study name to jump to its detailed table under "Conditions and results, study by study" below. The conditions of the test, the significance level and any disagreement between the text and the figures or tables are not shown in this overview but in the note under each row of that detailed table.
Results in which people rated bitterness only. Where each value comes from (a table or a reading from a figure) is shown in its row; scales and methods differ between studies, so compare within a row, not across rows.
| Study | Comparison and condition | Measured as | Condition named first (reference: no or short contact, seeds kept, low alcohol) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) | Direction / test |
|---|---|---|---|---|---|
| Lisjak 2020 | Seed extract in the model wine liquid: 3 days vs 20 days of extraction Seeds only of 2016 Cabernet Sauvignon soaked in a model wine liquid of 12% ethanol, pH 3.2 at 30 °C (3 replicates per day); ethanol held constant | rank sum of the order from least to most bitter (larger means ranked as more bitter; 7 people; the scale is described as 0–7 points but the table numbers are rank sums) | 11 (3 days) | 27 (20 days) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) more bitter Tested, significant |
| Lisjak 2020 | Seed extract in the model wine liquid: 5 days vs 20 days of extraction Seeds only of 2016 Cabernet Sauvignon soaked in a model wine liquid of 12% ethanol, pH 3.2 at 30 °C (3 replicates per day); ethanol held constant | rank sum of the order from least to most bitter (larger means ranked as more bitter; 7 people; the scale is described as 0–7 points but the table numbers are rank sums) | 10 (5 days) | 27 (20 days) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) more bitter Tested, significant |
| Lisjak 2020 | Skin extract in the model wine liquid: 3 days vs 20 days of extraction [text and table letters disagree] Skins only of 2016 Cabernet Sauvignon soaked in a model wine liquid of 12% ethanol, pH 3.2 at 30 °C (3 replicates per day); ethanol held constant | rank sum of the order from least to most bitter (larger means ranked as more bitter; 7 people; the scale is described as 0–7 points but the table numbers are rank sums) | 19 (3 days) | 21 (20 days) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) more bitter Tested, not significant |
| Lisjak 2020 | Wine during fermentation: day 3 vs day 15 [ethanol also rises with fermentation] Wine from 2016 Cabernet Sauvignon fermented in 3 concrete tanks of 7 tonnes, compared on day 3 and day 15 (ethanol also rises, to 0.6% on day 3 and 14.2% on day 15, as fermentation proceeds) | rank sum of the order from least to most bitter (larger means ranked as more bitter; 7 people; the scale is described as 0–7 points but the table numbers are rank sums) | 7 (day 3) | 30 (day 15) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) more bitter Tested, significant |
| Lisjak 2020 | Wine during fermentation: day 5 vs day 15 [ethanol also rises with fermentation] Wine from 2016 Cabernet Sauvignon fermented in 3 concrete tanks of 7 tonnes, compared on day 5 and day 15 (ethanol also rises, to 0.6% on day 3 and 14.2% on day 15, as fermentation proceeds) | rank sum of the order from least to most bitter (larger means ranked as more bitter; 7 people; the scale is described as 0–7 points but the table numbers are rank sums) | 10 (day 5) | 30 (day 15) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) more bitter Tested, significant |
| Aleixandre-Tudo 2015 | Contact with the skins before fermentation (4 °C, 12 hours): control vs ScBF Chenin Blanc (white) pressed at once after crushing (control) or left on the skins for 12 hours at 4 °C after crushing and then pressed (ScBF); both fermented at 15 °C with the same yeast; 3 replicates each | mean bitterness (descriptive analysis on a 10 cm line scale; the source gives no unit; higher is more bitter; 10 panellists, 3 repetitions) | 30.36 (control) | 31.16 (ScBF) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) more bitter Tested, not significant |
| Aleixandre-Tudo 2015 | Fermentation on the skins for the whole fermentation: control vs FoS [other differences besides the skins] Chenin Blanc (white) pressed at once after crushing (control) or fermented for the whole fermentation on the skins (mixed daily, pressed after fermentation) (FoS); both fermented at 15 °C with the same yeast; 3 replicates each | mean bitterness (descriptive analysis on a 10 cm line scale; the source gives no unit; higher is more bitter; 10 panellists, 3 repetitions) | 30.36 (control) | 46.70 (FoS) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) more bitter Tested, significant |
| Pazos 2026 | Maceration: control (10 days on the skins) vs extended (8 months) [main effect] Main effect of maceration alone, averaged over the 3 harvests and 3 alcohol levels of the 36 Cabernet Sauvignon (2019 vintage) wines rated; the control is 10 days on the skins and then pressed, extended is 8 months | mean bitterness (line scale with "low" and "high" at the ends; the maximum is not stated in the excerpt; higher is more bitter; 11 panellists) | 37.61 (control) | 46.83 (extended) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) more bitter Tested, significant |
| Jagatić Korenika 2023 | Plavac mali 2014 vintage: maceration of 7 days vs 49 days Plavac mali (red, 2014 vintage) made in 5 treatments: maceration of 7 days (control), 21 days and 49 days, and 21 and 49 days with seeds removed (85–90% of the seeds), 3 replicates each. Compares 7 days and 49 days | mean bitterness (5-step QDA, 0 = not perceptible … 5 = strongly perceptible; higher is more bitter; 7 experts, 3 repetitions) | 4.23 (7 days) | 4.81 (49 days) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) more bitter Tested, significant |
| Jagatić Korenika 2023 | Plavac mali 2015 vintage: maceration of 7 days vs 49 days [the difference is a small 0.07] Plavac mali (red, 2015 vintage) made in 5 treatments: maceration of 7 days (control), 21 days and 49 days, and 21 and 49 days with seeds removed (85–90% of the seeds), 3 replicates each. Compares 7 days and 49 days | mean bitterness (5-step QDA, 0 = not perceptible … 5 = strongly perceptible; higher is more bitter; 7 experts, 3 repetitions) | 3.54 (7 days) | 3.61 (49 days) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) more bitter Tested, significant |
| Jagatić Korenika 2023 | Plavac mali 2014 vintage: maceration of 7 days vs 21 days Plavac mali (red, 2014 vintage) made in 5 treatments: maceration of 7 days (control), 21 days and 49 days, and 21 and 49 days with seeds removed (85–90% of the seeds), 3 replicates each. Compares 7 days and 21 days | mean bitterness (5-step QDA, 0 = not perceptible … 5 = strongly perceptible; higher is more bitter; 7 experts, 3 repetitions) | 4.23 (7 days) | 4.33 (21 days) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) more bitter Tested, not significant |
| Jagatić Korenika 2023 | Plavac mali 2015 vintage: maceration of 7 days vs 21 days Plavac mali (red, 2015 vintage) made in 5 treatments: maceration of 7 days (control), 21 days and 49 days, and 21 and 49 days with seeds removed (85–90% of the seeds), 3 replicates each. Compares 7 days and 21 days | mean bitterness (5-step QDA, 0 = not perceptible … 5 = strongly perceptible; higher is more bitter; 7 experts, 3 repetitions) | 3.54 (7 days) | 3.57 (21 days) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) more bitter Tested, not significant |
| Orbanić 2023 | Teran (red): standard 7 days vs 5 treatments with a 48-hour pre-treatment and extended maceration (15 or 30 days in total) [values per treatment in a figure only] 6 treatments compared for bitterness by one-way ANOVA: K7 (standard 7 days), C15 and C30 (cooled at 8 °C for 48 hours, then 13 or 28 days from the start of fermentation and maceration to the end of extended maceration; 15 or 30 days in total including the pre-treatment), H15 and H30 (heated at 50 °C for 48 hours, then the same periods) and CS15 (cooled, then saignée, 13 days; 15 days in total) | bitterness score (10-point structured scale, 0 = not perceptible … 10 = strongly perceptible; higher is more bitter; 7 experts) | The K7 value is in Fig. 2 only (Figure not obtained, so values unconfirmed) | The values of the 5 treatments are also in Fig. 2 only (Figure not obtained, so values unconfirmed); the range over all 6 treatments is 3.86–4.45 (text) | Direction not given Tested, not significant |
| Blackford 2026 | Divona (white): direct pressing vs 12 hours of pre-fermentation maceration at 12 °C [no mean per group, no technical replicates] Divona from 3 vintages (2019, 2020 and 2022) compared with direct pressing and with 12 hours of pre-fermentation maceration at 12 °C after crushing (linear mixed model over fermentation temperatures of 15 °C and 20 °C) | bitterness score (line scale from 1 = no perception to 7 = very intense; higher is more bitter; 12 experienced tasters, 2 ratings) | Not given (the mean for direct pressing is not in the source; the overall mean is 2.4 ± 0.8) | Not given (the mean for pre-fermentation maceration is not in the source) | Direction not given Tested, not significant |
| Magrini 2016 | Sangiovese (red): standard fermentation vs cold soak for 48 hours or cryomaceration [no values] A trial with 3 replicates in which standard fermentation (CTRL), cold soak at 5 °C for 48 hours (CSPF) and cryomaceration with liquid nitrogen (CRYO) were crossed with fermentation temperatures of 20 and 30 °C and with saignée or not; cumulative link mixed model | bitterness rating (4 levels; the source calls it a hedonistic scale, and the definition of the levels and which end is higher are unconfirmed, so it is not confirmed to be an intensity scale; 15 people involved in the experiment) | Not given (no values are shown) | Not given (no values are shown) | Direction not given Tested, not significant |
| Stoffel 2025 | Syrah (red): reference (punch down, not chaptalised) vs extended maceration (rated at 3 months) [no individual result for bitterness; answers relative to a reference] With the punch-down (2 times a day), non-chaptalised wine (PD_Nat) as the reference (the Pivot), extended maceration (EM; half of the punch-down control tanks left for up to 6 months, rated at 3 months) without chaptalisation (EM_Nat) and with chaptalisation (EM_Chap) was compared with the reference in a modified Pivot Profile | choice of whether bitterness was "less than" or "more than" the reference (a multiple-choice questionnaire of attributes chosen in advance; 15 winemakers, with a 2-hour training on the procedure and attributes on the day of evaluation) | Not given (the reference wine PD_Nat; it is the reference and is not itself rated) | Not given (the numbers of bitterness answers for EM_Nat and EM_Chap are not shown) | Direction not given Test method described; result for this comparison not reported |
| Iino 2004 | Koshu (white): fermentation as juice vs skin-contact fermentation (3 days at 25 °C or 5 days at 15 °C) [yes or no only, no numbers of people, 5 people, no test; no direction label (no numbers)] 200 kg of Koshu grapes divided into 28 kg lots: juice fermentation pressed at once after crushing (J-25 and J-15) versus skin-contact fermentation mixed with the skins and seeds for 3 days at 25 °C (M-25) or 5 days at 15 °C (M-15) | whether a bitter aftertaste was pointed out (the entry in the taste column of Table 2; 5 expert panellists; the number of people who pointed it out and an intensity score are not shown) | Juice fermentation (J-25 and J-15): "bitterness as aftertaste" in the taste column of Table 2 | Skin-contact fermentation (M-25 and M-15): "—" in the taste column of Table 2 | Direction not given No test reported |
| Sancho-Galán 2021 | Palomino Fino (white): skins added during fermentation at 0% vs 100% [values in a figure only; no direction label (values not checked); no test result for bitterness in this pair] Skins added during fermentation of Palomino Fino (white) at 0 (control) to 100% of the must by volume (2 replicate 5 L fermentations, 18 °C, 21 days), rated by 20 experienced people on a 10-point scale 5 days after bottling; 0% is compared with 100% | bitterness score (10-point scale; higher is more bitter; 20 experienced people; values are in the radar chart of Fig. 4 only) | Only a rough visual reading of the figure, so not used (the text says the control was lowest) | Only a rough visual reading of the figure, so not used (the text says 100% was highest) | Direction not given Test method described; result for this comparison not reported |
| Philipp 2024 | Grüner Veltliner (white): direct pressing vs fermentation on the skins [no test, 1 pooled CATA sample; no direction label (numbers of mentions not obtained)] Direct pressing (C) and fermentation on the skins (PMF and FMF; 15 °C and 25 °C) of Grüner Veltliner (white), compared by 24 experts in CATA (the 3 replicates pooled into 1 sample) | number of times bitterness was ticked (CATA, check all that apply; 24 experts) | The number of mentions of bitterness is in a supplementary table only (supplementary table not obtained, so values unconfirmed) | The number of mentions of bitterness is in a supplementary table only (supplementary table not obtained, so values unconfirmed) | Direction not given No test reported |
| Yuan 2025 | Merlot (red): stored without pomace vs stored with prolonged pomace contact [the direction for pomace contact alone cannot be read; crossed with microwave treatment; no test; values in a figure only] Merlot (2022 vintage) stored in 2 ways, either with the skins and seeds filtered off after fermentation (no pomace) or with the pomace left in prolonged contact, crossed with 4 microwave treatment levels, 8 treatments in all, evaluated after 120 days of storage | bitterness score (10 cm line scale, 0 = no sensation … 10 = extremely high; higher is more bitter; 10 trained assessors) | In the radar chart of Fig. 4b only (Figure not obtained, so values unconfirmed) | In the radar chart of Fig. 4b only (Figure not obtained, so values unconfirmed) | Direction not given No test reported |
| Sokolowsky 2015 | Riesling and Gewürztraminer (white): wines made with different skin contact times [abstract only, no values; no direction label (no values)] Riesling and Gewürztraminer (2009 and 2010 vintages) made with different skin contact times (including a wine fermented completely on the skins) and evaluated by descriptive analysis (DA), time-intensity analysis (TI) and temporal dominance of sensations (TDS) | Not given (no scale or number of people in the abstract) | Not given (no values in the abstract) | Not given (no values in the abstract) | Direction not given Tested, significant |
| Jagatić Korenika 2023 | Seed removal: Plavac mali 2014 vintage: 21 days vs 21 days with seeds removed Plavac mali (red, 2014 vintage) made in 5 treatments: maceration of 7 days (control), 21 days and 49 days, and 21 and 49 days with seeds removed (85–90% of the seeds), 3 replicates each. Compares 21 days (seeds kept) and 21 days with seeds removed | mean bitterness (5-step QDA, 0 = not perceptible … 5 = strongly perceptible; higher is more bitter; 7 experts, 3 repetitions) | 4.33 (21 days, seeds kept) | 3.71 (21 days, seeds removed) | Condition named first (reference: no or short contact, seeds kept, low alcohol) more bitter Tested, significant |
| Jagatić Korenika 2023 | Seed removal: Plavac mali 2015 vintage: 21 days vs 21 days with seeds removed Plavac mali (red, 2015 vintage) made in 5 treatments: maceration of 7 days (control), 21 days and 49 days, and 21 and 49 days with seeds removed (85–90% of the seeds), 3 replicates each. Compares 21 days (seeds kept) and 21 days with seeds removed | mean bitterness (5-step QDA, 0 = not perceptible … 5 = strongly perceptible; higher is more bitter; 7 experts, 3 repetitions) | 3.57 (21 days, seeds kept) | 3.37 (21 days, seeds removed) | Condition named first (reference: no or short contact, seeds kept, low alcohol) more bitter Tested, significant |
| Jagatić Korenika 2023 | Seed removal: Plavac mali 2014 vintage: 49 days vs 49 days with seeds removed Plavac mali (red, 2014 vintage) made in 5 treatments: maceration of 7 days (control), 21 days and 49 days, and 21 and 49 days with seeds removed (85–90% of the seeds), 3 replicates each. Compares 49 days (seeds kept) and 49 days with seeds removed | mean bitterness (5-step QDA, 0 = not perceptible … 5 = strongly perceptible; higher is more bitter; 7 experts, 3 repetitions) | 4.81 (49 days, seeds kept) | 3.56 (49 days, seeds removed) | Condition named first (reference: no or short contact, seeds kept, low alcohol) more bitter Tested, significant |
| Jagatić Korenika 2023 | Seed removal: Plavac mali 2015 vintage: 49 days vs 49 days with seeds removed Plavac mali (red, 2015 vintage) made in 5 treatments: maceration of 7 days (control), 21 days and 49 days, and 21 and 49 days with seeds removed (85–90% of the seeds), 3 replicates each. Compares 49 days (seeds kept) and 49 days with seeds removed | mean bitterness (5-step QDA, 0 = not perceptible … 5 = strongly perceptible; higher is more bitter; 7 experts, 3 repetitions) | 3.61 (49 days, seeds kept) | 3.49 (49 days, seeds removed) | Condition named first (reference: no or short contact, seeds kept, low alcohol) more bitter Tested, significant |
| Pazos 2026 | Alcohol (not a contact variable): low (about 10.5%) vs high (about 16.5%) [main effect] Main effect of alcohol alone, averaged over all maceration and harvest levels; alcohol was adjusted by chaptalisation (sucrose) or dilution (tartaric acid water) to about 10.5, 13.5 and 16.5% | mean bitterness (line scale with "low" and "high" at the ends; the maximum is not stated in the excerpt; higher is more bitter; 11 panellists) | 35.55 (low) | 47.13 (high) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) more bitter Tested, significant |
| Pazos 2026 | Alcohol (not a contact variable): medium (about 13.5%) vs high (about 16.5%) [main effect] Main effect of alcohol alone, averaged over all maceration and harvest levels; alcohol was adjusted by chaptalisation (sucrose) or dilution (tartaric acid water) to about 10.5, 13.5 and 16.5% | mean bitterness (line scale with "low" and "high" at the ends; the maximum is not stated in the excerpt; higher is more bitter; 11 panellists) | 43.97 (medium) | 47.13 (high) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) more bitter Tested, not significant |
| Fontoin 2008 | Alcohol (not a contact variable): varying ethanol in a model wine solution (including 11–15%) [abstract only, no values, a solution and not wine] In a model wine solution with oligomeric tannins from grape seeds, pH, ethanol and tartaric acid concentration were varied one at a time and 16 judges rated bitterness and astringency | Not given (no scale in the abstract; 16 judges) | Not given (no values in the abstract) | Not given (no values in the abstract) | Direction not given No test reported |
| Iino 2004 | Substance threshold (ethanol solution): ethyl caprylate 0 vs 0.75 mg/L (ethanol 8%) [difference in ethyl caprylate concentration; not a comparison of contact] 8% ethanol solutions with ethyl caproate at 1 mg/L (added to all to mask aroma) and ethyl caprylate, with 14 people indicating whether they perceived a strong lingering bitter aftertaste; ethyl caprylate at 0 (control) and 0.75 mg/L | number of people pointing out a strong lingering bitter aftertaste (of 14; higher means more people found it bitter) | 0 people (0 mg/L) | 11 people (0.75 mg/L, of 14) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) higher Test method described; result for this comparison not reported |
| Iino 2004 | Substance threshold (ethanol solution): ethanol 4% vs 8% (ethyl caprylate 2 mg/L) [difference in ethanol concentration; not a comparison of contact] Ethanol solutions containing ethyl caprylate at 2 mg/L and ethyl caproate at 1 mg/L at ethanol concentrations of 4, 6, 8, 10 and 12%, with 20 people indicating whether they perceived a strong lingering bitter aftertaste; 4% is compared with 8% | number of people pointing out a strong lingering bitter aftertaste (of 20; higher means more people found it bitter) | 0 people (4%) | 15 people (8%, of 20) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) higher Test method described; result for this comparison not reported |
Conditions and results, study by study
For each study, the grapes and conditions of contact, how samples were served and who rated them, and the results. Each row is one study × one measured result, so different comparisons in the same study are separate rows. Under each row we give where it is in the paper and whether it can be used to judge whether, for the same grapes (or the same model wine liquid), changing only the length or method of contact with the skins and seeds changes the intensity of bitterness people perceive, with the reason. Where something other than the length of contact changed together (alcohol, sugar, pH, acidity, the temperature of a pre-treatment) or where the test was in a solution and not wine, the reason says so. Nothing is left blank: "not given", "not read" and "not applicable" are kept apart, and values from figures we did not obtain are marked as such. Where the text and the figures or tables of a study disagree, the disagreement is kept.
Lisjak 2020 sensory only
Effect of extraction time on content, composition and sensory perception of proanthocyanidins in wine‐like medium and during industrial fermentation of Cabernet Sauvignon. J Sci Food Agric 100(5) — doi:10.1002/jsfa.10189
- How deeply checked
- Checked in full text — Full text via the Europe PMC XML (text and Tables 2–4); Figs 3 and 4 (PCA) not viewed Checked by: LLM (one extracted, another checked against the source; no human check), 2026-10-23.
- Samples
- Cabernet Sauvignon (2016 vintage, Macedonia). (a) Extracts made by soaking skins only or seeds only for 3, 5, 7, 10, 15 and 20 days in a model wine liquid (ethanol 12%, pH 3.2, 30 °C), 3 replicates per day. (b) Wine from 3 concrete tanks of 7 tonnes sampled on days 3, 5, 7, 9, 11, 13 and 15 of fermentation (ethanol also rises from 0.6% to 14.2% as fermentation proceeds; the methods say concrete and the last paragraph of the introduction says stainless-steel, so the source disagrees with itself)
- Processing and cooking
- Not applicable (only the days of contact were varied); fermentation at 25 °C after 2 days at 10–15 °C before fermentation, 3 délestages, and the free-run wine drawn off after 15 days
- How it was served or eaten
- Room temperature (20 ± 2 °C) in OIV glasses in random order with at least 30 s between samples; ranking test (samples ordered from least to most bitter)
- Who rated, on what scale
- 7 professional wine tasters and oenologists at the winery, trained with quinine sulfate (0.05, 0.1 and 0.2 g/L) for bitterness and aluminium sulfate for astringency; the scale is described as 0–7 points but the numbers in the tables are rank sums; Friedman test then LSD (5%)
| Measured | Comparison and condition | Condition named first (reference: no or short contact, seeds kept, low alcohol) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) | Unit | Direction / test |
|---|---|---|---|---|---|
| Bitterness intensity (sensory) | Seed extract in the model wine liquid: 3 days vs 20 days of extraction Seeds only of 2016 Cabernet Sauvignon soaked in a model wine liquid of 12% ethanol, pH 3.2 at 30 °C (3 replicates per day); ethanol held constant | 11 (3 days) | 27 (20 days) | rank sum of the order from least to most bitter (larger means ranked as more bitter; 7 people; the scale is described as 0–7 points but the table numbers are rank sums) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) more bitter Tested, significant |
| Direction shows which published value is larger. In Table 2 the letters are a for 3 days and b for 20 days (LSD 5%), and the text says seed astringency and bitterness after 15 and 20 days were significantly higher than after 3 and 5 days. 15 days is 24 (b). The columns of Table 2 each sum to 111 (6 samples), which does not look like the total expected if 7 people ranked all samples, but how the ranks were assigned is not described and the cause is not guessed at. Seeds and skins were ranked separately, so the numbers cannot be compared between seeds and skins. Astringency moves in the same direction (rated as a separate item). The authors relate the higher astringency of seed extracts after longer extraction to a rise in the amount of high- and low-molecular-weight proanthocyanidins (a correlation in a PCA; the figure was not viewed) Where: Results and discussion (sensory evaluation of skin and seed extracts in the model wine liquid), Table 2 For whether changing only the length or method of contact with the skins and seeds (days of extraction, skin maceration, fermentation on the skins, removal of seeds) for the same grapes (or the same model wine liquid) changes the intensity of bitterness people perceive: Usable — The same seeds were soaked in a model wine liquid with ethanol, pH and temperature held constant and only the number of days varied, ranked by the same 7 people, with a test; but it is an extract of seeds only, not a wine | |||||
| Bitterness intensity (sensory) | Seed extract in the model wine liquid: 5 days vs 20 days of extraction Seeds only of 2016 Cabernet Sauvignon soaked in a model wine liquid of 12% ethanol, pH 3.2 at 30 °C (3 replicates per day); ethanol held constant | 10 (5 days) | 27 (20 days) | rank sum of the order from least to most bitter (larger means ranked as more bitter; 7 people; the scale is described as 0–7 points but the table numbers are rank sums) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) more bitter Tested, significant |
| Direction shows which published value is larger. In Table 2 the letters are a for 5 days and b for 20 days (LSD 5%), and the text says seed astringency and bitterness after 15 and 20 days were significantly higher than after 3 and 5 days. 15 days is 24 (b). The columns of Table 2 each sum to 111 (6 samples), which does not look like the total expected if 7 people ranked all samples, but how the ranks were assigned is not described and the cause is not guessed at. Seeds and skins were ranked separately, so the numbers cannot be compared between seeds and skins. Astringency moves in the same direction (rated as a separate item). The authors relate the higher astringency of seed extracts after longer extraction to a rise in the amount of high- and low-molecular-weight proanthocyanidins (a correlation in a PCA; the figure was not viewed) Where: Results and discussion (sensory evaluation of skin and seed extracts in the model wine liquid), Table 2 For whether changing only the length or method of contact with the skins and seeds (days of extraction, skin maceration, fermentation on the skins, removal of seeds) for the same grapes (or the same model wine liquid) changes the intensity of bitterness people perceive: Usable — The same seeds were soaked in a model wine liquid with ethanol, pH and temperature held constant and only the number of days varied, ranked by the same 7 people, with a test; but it is an extract of seeds only, not a wine | |||||
| Bitterness intensity (sensory) | Skin extract in the model wine liquid: 3 days vs 20 days of extraction [text and table letters disagree] Skins only of 2016 Cabernet Sauvignon soaked in a model wine liquid of 12% ethanol, pH 3.2 at 30 °C (3 replicates per day); ethanol held constant | 19 (3 days) | 21 (20 days) | rank sum of the order from least to most bitter (larger means ranked as more bitter; 7 people; the scale is described as 0–7 points but the table numbers are rank sums) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) more bitter Tested, not significant |
| Direction shows which published value is larger. The letters in Table 2 for this pair are both ab, and the text also says the skin extracts showed no significant difference in colour, astringency or bitterness across days. However, the letters in Table 2 differ between 5 days (12, a) and 7 days (24, b) for bitterness, between 10 days (a) and 20 days (b) for astringency and between 5 days (b) and 7 days (a) for colour, so the text and the table disagree; the cause is not given in the source Where: Results and discussion (sensory evaluation of skin and seed extracts in the model wine liquid), Table 2 For whether changing only the length or method of contact with the skins and seeds (days of extraction, skin maceration, fermentation on the skins, removal of seeds) for the same grapes (or the same model wine liquid) changes the intensity of bitterness people perceive: Limited — The comparison is under the same conditions, but the text says the skin extracts showed no significant difference across days while the letters in the table show differences for other pairs of days, so they disagree; for this pair neither the text nor the table shows a difference | |||||
| Bitterness intensity (sensory) | Wine during fermentation: day 3 vs day 15 [ethanol also rises with fermentation] Wine from 2016 Cabernet Sauvignon fermented in 3 concrete tanks of 7 tonnes, compared on day 3 and day 15 (ethanol also rises, to 0.6% on day 3 and 14.2% on day 15, as fermentation proceeds) | 7 (day 3) | 30 (day 15) | rank sum of the order from least to most bitter (larger means ranked as more bitter; 7 people; the scale is described as 0–7 points but the table numbers are rank sums) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) more bitter Tested, significant |
| Direction shows which published value is larger. In Table 4 the letters are a for day 3 and c for day 15 (LSD 5%), and the text says bitterness on days 3 and 5 was significantly lower than on days 11, 13 and 15. Day 11 is 30 (c) and day 13 is 32 (c). Ethanol is 0.6% on day 3 and 14.2% on day 15 (Table 3), and the authors write that perceived bitterness in fermenting wine may also depend on changes in alcohol and sugar (the extraction in the model liquid was set up to avoid this). Whether the bitterness ratings are the mean of the 3 tanks is not stated in the source and was not confirmed. The material of the tanks is inconsistent in the source (the methods say concrete, the last paragraph of the introduction says stainless-steel). The bitterness column of Table 4 sums to 147 (7 samples), which does not look like the total expected if 7 people ranked all samples, and the cause is not guessed at. The wine samples were frozen at −20 °C and analysed 6 months later (whether the same applies to the sensory evaluation was not checked). Astringency moves in the same direction (rated as a separate item) Where: Results and discussion (sensory evaluation of fermented wines), Tables 3 and 4 For whether changing only the length or method of contact with the skins and seeds (days of extraction, skin maceration, fermentation on the skins, removal of seeds) for the same grapes (or the same model wine liquid) changes the intensity of bitterness people perceive: Limited — Not only the days of contact but also ethanol and sugar change at the same time, so the effect of the length of contact cannot be separated; wines fermented in 7-tonne tanks, with a test | |||||
| Bitterness intensity (sensory) | Wine during fermentation: day 5 vs day 15 [ethanol also rises with fermentation] Wine from 2016 Cabernet Sauvignon fermented in 3 concrete tanks of 7 tonnes, compared on day 5 and day 15 (ethanol also rises, to 0.6% on day 3 and 14.2% on day 15, as fermentation proceeds) | 10 (day 5) | 30 (day 15) | rank sum of the order from least to most bitter (larger means ranked as more bitter; 7 people; the scale is described as 0–7 points but the table numbers are rank sums) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) more bitter Tested, significant |
| Direction shows which published value is larger. In Table 4 the letters are a,b for day 5 and c for day 15 (LSD 5%), and the text says bitterness on days 3 and 5 was significantly lower than on days 11, 13 and 15. Day 11 is 30 (c) and day 13 is 32 (c). Ethanol is 0.6% on day 3 and 14.2% on day 15 (Table 3), and the authors write that perceived bitterness in fermenting wine may also depend on changes in alcohol and sugar (the extraction in the model liquid was set up to avoid this). Whether the bitterness ratings are the mean of the 3 tanks is not stated in the source and was not confirmed. The material of the tanks is inconsistent in the source (the methods say concrete, the last paragraph of the introduction says stainless-steel). The bitterness column of Table 4 sums to 147 (7 samples), which does not look like the total expected if 7 people ranked all samples, and the cause is not guessed at. The wine samples were frozen at −20 °C and analysed 6 months later (whether the same applies to the sensory evaluation was not checked). Astringency moves in the same direction (rated as a separate item) Where: Results and discussion (sensory evaluation of fermented wines), Tables 3 and 4 For whether changing only the length or method of contact with the skins and seeds (days of extraction, skin maceration, fermentation on the skins, removal of seeds) for the same grapes (or the same model wine liquid) changes the intensity of bitterness people perceive: Limited — Not only the days of contact but also ethanol and sugar change at the same time, so the effect of the length of contact cannot be separated; wines fermented in 7-tonne tanks, with a test | |||||
Aleixandre-Tudo 2015 sensory only
Effect of Skin Contact Before and During Alcoholic Fermentation on the Chemical and Sensory Profile of South African Chenin Blanc White Wines. South African Journal of Enology and Viticulture 36(3):366-377 — doi:10.21548/36-3-969
- How deeply checked
- Checked in full text — Full text via the SAJEV PDF (methods, Tables 2 and 5, discussion); an existing ledger source whose Table 5 values were rechecked for this question Checked by: LLM (one extracted, another checked against the source; no human check), 2026-10-23.
- Samples
- Chenin Blanc (white, 2013 vintage, Stellenbosch). The same grapes (25.6 °B, pH 3.40, total acidity 6.38 g/L) were divided into 3 treatments: control (destemmed, crushed and pressed at once), ScBF (4 °C for 12 hours on the skins after crushing, then pressed) and FoS (fermented on the skins for the whole fermentation, mixed once a day, pressed after fermentation); 3 replicates each, 9 wines in all
- Processing and cooking
- Not applicable (only the length and method of contact were varied); all fermentations at 15 °C with the same yeast (QA23); evaluated after a year of bottle storage
- How it was served or eaten
- Coded with random three-digit numbers to avoid order bias; unstructured 10 cm line scale (from none to intense), 3 repetitions; the table values look like 0–100 but the source gives no unit
- Who rated, on what scale
- 10 trained panellists (3 men, 7 women, mean age 28), descriptive analysis; LSD (Fisher) test at p<0.05, with p values and significance marks in Table 5
| Measured | Comparison and condition | Condition named first (reference: no or short contact, seeds kept, low alcohol) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) | Unit | Direction / test |
|---|---|---|---|---|---|
| Bitterness intensity (sensory) | Contact with the skins before fermentation (4 °C, 12 hours): control vs ScBF Chenin Blanc (white) pressed at once after crushing (control) or left on the skins for 12 hours at 4 °C after crushing and then pressed (ScBF); both fermented at 15 °C with the same yeast; 3 replicates each | 30.36 (control) | 31.16 (ScBF) | mean bitterness (descriptive analysis on a 10 cm line scale; the source gives no unit; higher is more bitter; 10 panellists, 3 repetitions) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) more bitter Tested, not significant |
| Direction shows which published value is larger. Table 5 gives the control and ScBF the same letter (a) (LSD Fisher, p<0.05), so no difference was shown for this pair. The p=0.000 (**) in Table 5 is the value of the test over all 3 groups, not the p value of this pair Where: Results and discussion (sensory profile by descriptive analysis), Table 5 For whether changing only the length or method of contact with the skins and seeds (days of extraction, skin maceration, fermentation on the skins, removal of seeds) for the same grapes (or the same model wine liquid) changes the intensity of bitterness people perceive: Usable — The same grapes were divided into 3 and only the presence of skin contact before fermentation was varied, rated by the same 10 people; for this pair the letters are the same (no difference shown); the p is the value over all 3 groups | |||||
| Bitterness intensity (sensory) | Fermentation on the skins for the whole fermentation: control vs FoS [other differences besides the skins] Chenin Blanc (white) pressed at once after crushing (control) or fermented for the whole fermentation on the skins (mixed daily, pressed after fermentation) (FoS); both fermented at 15 °C with the same yeast; 3 replicates each | 30.36 (control) | 46.70 (FoS) | mean bitterness (descriptive analysis on a 10 cm line scale; the source gives no unit; higher is more bitter; 10 panellists, 3 repetitions) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) more bitter Tested, significant |
| Direction shows which published value is larger. Table 5 gives p=0.000 (**) over all 3 groups, and by the LSD (Fisher, p<0.05) FoS has a different letter (b). This p is the value over all 3 groups, not a p value for each pair (it does not say "p<0.001"). There are differences besides the skins (Table 2): pH is 3.34 for FoS and 3.39 for the control (p=0.004), total acidity 6.23 against 5.52 and fructose 1.77 against 7.92 mg/L (the unit of total acidity disagrees: g/L in the methods and mg/L in the note to Table 2; fructose is mg/L in both). Ethanol did not differ significantly: 15.74% for the control, 15.76% for ScBF and 16.06% for FoS (p=0.325). The text says FoS was rated more astringent, more bitter and more sour, and the authors guess that lower pH, higher acidity and more phenolics may have been involved (not checked). Astringency is 25.76 (a) for the control, 26.00 (a) for ScBF and 41.33 (b) for FoS, with p=0.010 over all 3 groups; no difference in astringency was shown between the control and ScBF Where: Results and discussion (sensory profile by descriptive analysis), Table 5 For whether changing only the length or method of contact with the skins and seeds (days of extraction, skin maceration, fermentation on the skins, removal of seeds) for the same grapes (or the same model wine liquid) changes the intensity of bitterness people perceive: Limited — The same grapes were fermented on the skins or not, but pH, total acidity and fructose also differ, so this cannot be called the effect of the skins alone; the p is the value over all 3 groups | |||||
Pazos 2026 sensory only
Impact of Harvest, Extended Maceration, and Alcohol on Sensory Profiles of Cabernet Sauvignon Wines. Beverages 12(3):30 — doi:10.3390/beverages12030030
- How deeply checked
- Checked in full text — Text and Tables 3 and 4 of the MDPI page read in the built-in browser and checked against the saved excerpt (only the excerpt is at hand); figures and supplements not viewed Checked by: LLM (one extracted, another checked against the source; no human check), 2026-10-23.
- Samples
- Cabernet Sauvignon (2019 vintage). 3 harvests at 20, 24 and 28 Brix; each must adjusted by chaptalisation (sucrose) or dilution (tartaric acid water) to about 10.5, 13.5 and 16.5% alcohol; maceration either the control (10 days on the skins, then pressed) or extended (8 months). 3 × 3 × 2 with 3 replicates, 54 wines, of which 36 wines (2 replicates each) were rated sensorially
- Processing and cooking
- Not applicable (the length of contact was varied); alcohol was adjusted by chaptalisation or dilution, so other components change too
- How it was served or eaten
- 2 years after bottling, each wine rated 3 times on an unstructured line scale with "low" and "high" at the ends (maximum not stated in the excerpt); bitterness standards were caffeine at 0.355, 1 and 2 g/L
- Who rated, on what scale
- 11 panellists (aged 22–55, most without wine experience), trained in 2 stages of 3 sessions; three-way ANOVA with the panellist as block and Tukey (p<0.05)
| Measured | Comparison and condition | Condition named first (reference: no or short contact, seeds kept, low alcohol) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) | Unit | Direction / test |
|---|---|---|---|---|---|
| Bitterness intensity (sensory) | Maceration: control (10 days on the skins) vs extended (8 months) [main effect] Main effect of maceration alone, averaged over the 3 harvests and 3 alcohol levels of the 36 Cabernet Sauvignon (2019 vintage) wines rated; the control is 10 days on the skins and then pressed, extended is 8 months | 37.61 (control) | 46.83 (extended) | mean bitterness (line scale with "low" and "high" at the ends; the maximum is not stated in the excerpt; higher is more bitter; 11 panellists) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) more bitter Tested, significant |
| Direction shows which published value is larger. In Table 4 (three-way ANOVA, Tukey, p<0.05) p<0.0001, with the letter b for the control and a for extended. Astringency is 35.31 against 63.72 (a separate item; p<0.0001). The interactions were not shown: maceration × alcohol p=0.8157, harvest × maceration p=0.1538 and the 3 factors together p=0.1505. The authors write that extended-maceration wines were associated with dried-fruit aroma, astringency and bitterness Where: Results and discussion (sensory), Table 4 For whether changing only the length or method of contact with the skins and seeds (days of extraction, skin maceration, fermentation on the skins, removal of seeds) for the same grapes (or the same model wine liquid) changes the intensity of bitterness people perceive: Usable — The main effect of maceration alone, with harvest and alcohol conditions the same, over 36 wines, with a test; it is a comparison of means pooled over levels, not a pairwise p | |||||
| Bitterness intensity (sensory) | Alcohol (not a contact variable): low (about 10.5%) vs high (about 16.5%) [main effect] Main effect of alcohol alone, averaged over all maceration and harvest levels; alcohol was adjusted by chaptalisation (sucrose) or dilution (tartaric acid water) to about 10.5, 13.5 and 16.5% | 35.55 (low) | 47.13 (high) | mean bitterness (line scale with "low" and "high" at the ends; the maximum is not stated in the excerpt; higher is more bitter; 11 panellists) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) more bitter Tested, significant |
| Direction shows which published value is larger. In Table 4 the letters are b for low, a for medium and a for high (p<0.0001), so low differs significantly from medium and high. The harvest × alcohol interaction is p=0.0018, and the main-effect means for alcohol average over it. Chaptalisation and dilution change other components too. The high-alcohol wines had difficulty finishing fermentation and had more residual sugar (the authors; the correlation of residual sugar with bitterness, 0.33, is not significant). The correlation of pH with bitterness is 0.54 (*). The authors note no correlation of bitterness with the proportion of monomers and guess that alcohol itself may be bitter (not checked). Another study that reconstituted the same deodorised red wine (Di Fede 2026) writes that bitterness was stronger and sourness weaker with higher ethanol and higher pH, but its bitterness values are in a figure only, pH and total acidity move together and lactones were added (that study is not a row of this table) Where: Results and discussion (sensory), Table 4 For whether changing only the length or method of contact with the skins and seeds (days of extraction, skin maceration, fermentation on the skins, removal of seeds) for the same grapes (or the same model wine liquid) changes the intensity of bitterness people perceive: Not usable — An alcohol axis that does not change contact with the skins and seeds, so it cannot be used for the comparison of contact (chaptalisation and dilution change other components too); shown as material for thinking about the effect of alcohol, which moves together with contact in some comparisons | |||||
| Bitterness intensity (sensory) | Alcohol (not a contact variable): medium (about 13.5%) vs high (about 16.5%) [main effect] Main effect of alcohol alone, averaged over all maceration and harvest levels; alcohol was adjusted by chaptalisation (sucrose) or dilution (tartaric acid water) to about 10.5, 13.5 and 16.5% | 43.97 (medium) | 47.13 (high) | mean bitterness (line scale with "low" and "high" at the ends; the maximum is not stated in the excerpt; higher is more bitter; 11 panellists) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) more bitter Tested, not significant |
| Direction shows which published value is larger. In Table 4 medium and high both have the letter a, so no difference was shown for this pair. The pair low and medium is 35.55 (b) against 43.97 (a), which differs significantly. The harvest × alcohol interaction is p=0.0018 (the main-effect means average over it) Where: Results and discussion (sensory), Table 4 For whether changing only the length or method of contact with the skins and seeds (days of extraction, skin maceration, fermentation on the skins, removal of seeds) for the same grapes (or the same model wine liquid) changes the intensity of bitterness people perceive: Not usable — An alcohol axis that does not change contact with the skins and seeds, so it cannot be used for the comparison of contact (chaptalisation and dilution change other components too); shown as material for thinking about the effect of alcohol, which moves together with contact in some comparisons | |||||
Jagatić Korenika 2023 sensory only
The Effect of Seed Removal and Extraction Time on the Phenolic Profile of Plavac Mali Wine. Appl Sci 13(9):5411 — doi:10.3390/app13095411
- How deeply checked
- Checked in full text — Methods and Tables 3 and 4 of the MDPI page read in the built-in browser and checked against the saved excerpt (only the excerpt is at hand); figures not viewed Checked by: LLM (one extracted, another checked against the source; no human check), 2026-10-23.
- Samples
- Plavac mali (red, 2014 and 2015 vintages). A maceration 7 days (control), B 21 days, C 49 days, D 21 days with seeds removed (85–90% of the seeds), E 49 days with seeds removed; 3 replicates each. The text says ethanol, acidity and pH did not differ much
- Processing and cooking
- Not applicable (days of contact and presence of seeds were varied)
- How it was served or eaten
- QDA on 5 steps (0 not perceptible to 5 strongly perceptible), 3 repetitions; a separate table for each vintage
- Who rated, on what scale
- 7 experts (the breakdown is not in the excerpt); one-way ANOVA with Duncan's test (letters; the level is not stated in the excerpt)
| Measured | Comparison and condition | Condition named first (reference: no or short contact, seeds kept, low alcohol) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) | Unit | Direction / test |
|---|---|---|---|---|---|
| Bitterness intensity (sensory) | Plavac mali 2014 vintage: maceration of 7 days vs 49 days Plavac mali (red, 2014 vintage) made in 5 treatments: maceration of 7 days (control), 21 days and 49 days, and 21 and 49 days with seeds removed (85–90% of the seeds), 3 replicates each. Compares 7 days and 49 days | 4.23 (7 days) | 4.81 (49 days) | mean bitterness (5-step QDA, 0 = not perceptible … 5 = strongly perceptible; higher is more bitter; 7 experts, 3 repetitions) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) more bitter Tested, significant |
| Direction shows which published value is larger. The Duncan test letters in Table 3 (the level is not stated in the excerpt; a separate test for each vintage) are b for 7 days and a for 49 days. Astringency goes the other way, 3.95 (7 days) against 3.71 (49 days) (letters a and b). Where: Results and discussion (sensory), Table 3 For whether changing only the length or method of contact with the skins and seeds (days of extraction, skin maceration, fermentation on the skins, removal of seeds) for the same grapes (or the same model wine liquid) changes the intensity of bitterness people perceive: Usable — The same grapes (same vintage) in the same trial with only the number of days of maceration varied, rated by the same 7 people; the test is Duncan's letters, and how the 3 repetitions of the 7 people were treated cannot be read from the excerpt | |||||
| Bitterness intensity (sensory) | Plavac mali 2015 vintage: maceration of 7 days vs 49 days [the difference is a small 0.07] Plavac mali (red, 2015 vintage) made in 5 treatments: maceration of 7 days (control), 21 days and 49 days, and 21 and 49 days with seeds removed (85–90% of the seeds), 3 replicates each. Compares 7 days and 49 days | 3.54 (7 days) | 3.61 (49 days) | mean bitterness (5-step QDA, 0 = not perceptible … 5 = strongly perceptible; higher is more bitter; 7 experts, 3 repetitions) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) more bitter Tested, significant |
| Direction shows which published value is larger. The Duncan test letters in Table 3 (the level is not stated in the excerpt; a separate test for each vintage) are b for 7 days and a for 49 days. The difference is a small 0.07. Whether the 3 repetitions of the 7 people were put into the analysis of variance as they are cannot be read from the excerpt. Astringency is 3.37 (7 days) against 3.23 (49 days). Where: Results and discussion (sensory), Table 3 For whether changing only the length or method of contact with the skins and seeds (days of extraction, skin maceration, fermentation on the skins, removal of seeds) for the same grapes (or the same model wine liquid) changes the intensity of bitterness people perceive: Usable — The same grapes (same vintage) in the same trial with only the number of days of maceration varied, rated by the same 7 people; the test is Duncan's letters, and how the 3 repetitions of the 7 people were treated cannot be read from the excerpt | |||||
| Bitterness intensity (sensory) | Plavac mali 2014 vintage: maceration of 7 days vs 21 days Plavac mali (red, 2014 vintage) made in 5 treatments: maceration of 7 days (control), 21 days and 49 days, and 21 and 49 days with seeds removed (85–90% of the seeds), 3 replicates each. Compares 7 days and 21 days | 4.23 (7 days) | 4.33 (21 days) | mean bitterness (5-step QDA, 0 = not perceptible … 5 = strongly perceptible; higher is more bitter; 7 experts, 3 repetitions) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) more bitter Tested, not significant |
| Direction shows which published value is larger. The Duncan test letters in Table 3 (the level is not stated in the excerpt; a separate test for each vintage) are b for both 7 days and 21 days, so no difference was shown. Where: Results and discussion (sensory), Table 3 For whether changing only the length or method of contact with the skins and seeds (days of extraction, skin maceration, fermentation on the skins, removal of seeds) for the same grapes (or the same model wine liquid) changes the intensity of bitterness people perceive: Usable — The same grapes (same vintage) in the same trial with only the number of days of maceration varied, rated by the same 7 people; the test is Duncan's letters, and how the 3 repetitions of the 7 people were treated cannot be read from the excerpt | |||||
| Bitterness intensity (sensory) | Plavac mali 2015 vintage: maceration of 7 days vs 21 days Plavac mali (red, 2015 vintage) made in 5 treatments: maceration of 7 days (control), 21 days and 49 days, and 21 and 49 days with seeds removed (85–90% of the seeds), 3 replicates each. Compares 7 days and 21 days | 3.54 (7 days) | 3.57 (21 days) | mean bitterness (5-step QDA, 0 = not perceptible … 5 = strongly perceptible; higher is more bitter; 7 experts, 3 repetitions) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) more bitter Tested, not significant |
| Direction shows which published value is larger. The Duncan test letters in Table 3 (the level is not stated in the excerpt; a separate test for each vintage) are b for 7 days and ab for 21 days, sharing b, so no difference was shown. Where: Results and discussion (sensory), Table 3 For whether changing only the length or method of contact with the skins and seeds (days of extraction, skin maceration, fermentation on the skins, removal of seeds) for the same grapes (or the same model wine liquid) changes the intensity of bitterness people perceive: Usable — The same grapes (same vintage) in the same trial with only the number of days of maceration varied, rated by the same 7 people; the test is Duncan's letters, and how the 3 repetitions of the 7 people were treated cannot be read from the excerpt | |||||
| Bitterness intensity (sensory) | Seed removal: Plavac mali 2014 vintage: 21 days vs 21 days with seeds removed Plavac mali (red, 2014 vintage) made in 5 treatments: maceration of 7 days (control), 21 days and 49 days, and 21 and 49 days with seeds removed (85–90% of the seeds), 3 replicates each. Compares 21 days (seeds kept) and 21 days with seeds removed | 4.33 (21 days, seeds kept) | 3.71 (21 days, seeds removed) | mean bitterness (5-step QDA, 0 = not perceptible … 5 = strongly perceptible; higher is more bitter; 7 experts, 3 repetitions) | Condition named first (reference: no or short contact, seeds kept, low alcohol) more bitter Tested, significant |
| Direction shows which published value is larger. The Duncan test letters in Table 3 (the level is not stated in the excerpt; a separate test for each vintage) are b for 21 days with seeds and c for seeds removed. Astringency also fell, from 3.85 to 3.13.Removing the seeds compares the presence of seeds, not the length of contact, so this is a different finding from the rise in bitterness with longer contact Where: Results and discussion (sensory), Table 3 For whether changing only the length or method of contact with the skins and seeds (days of extraction, skin maceration, fermentation on the skins, removal of seeds) for the same grapes (or the same model wine liquid) changes the intensity of bitterness people perceive: Usable — A comparison of a method included in the question (seed removal): the same grapes, the same vintage and the same number of days with only 85–90% of the seeds removed, rated by the same 7 people. It is read as the effect of the presence of seeds, separately from the effect of the length of contact. The test is Duncan's letters, and how the 3 repetitions of the 7 people were treated cannot be read from the excerpt | |||||
| Bitterness intensity (sensory) | Seed removal: Plavac mali 2015 vintage: 21 days vs 21 days with seeds removed Plavac mali (red, 2015 vintage) made in 5 treatments: maceration of 7 days (control), 21 days and 49 days, and 21 and 49 days with seeds removed (85–90% of the seeds), 3 replicates each. Compares 21 days (seeds kept) and 21 days with seeds removed | 3.57 (21 days, seeds kept) | 3.37 (21 days, seeds removed) | mean bitterness (5-step QDA, 0 = not perceptible … 5 = strongly perceptible; higher is more bitter; 7 experts, 3 repetitions) | Condition named first (reference: no or short contact, seeds kept, low alcohol) more bitter Tested, significant |
| Direction shows which published value is larger. The Duncan test letters in Table 3 (the level is not stated in the excerpt; a separate test for each vintage) are ab for 21 days with seeds and c for seeds removed. Astringency also fell, from 3.18 to 3.04.Removing the seeds compares the presence of seeds, not the length of contact, so this is a different finding from the rise in bitterness with longer contact Where: Results and discussion (sensory), Table 3 For whether changing only the length or method of contact with the skins and seeds (days of extraction, skin maceration, fermentation on the skins, removal of seeds) for the same grapes (or the same model wine liquid) changes the intensity of bitterness people perceive: Usable — A comparison of a method included in the question (seed removal): the same grapes, the same vintage and the same number of days with only 85–90% of the seeds removed, rated by the same 7 people. It is read as the effect of the presence of seeds, separately from the effect of the length of contact. The test is Duncan's letters, and how the 3 repetitions of the 7 people were treated cannot be read from the excerpt | |||||
| Bitterness intensity (sensory) | Seed removal: Plavac mali 2014 vintage: 49 days vs 49 days with seeds removed Plavac mali (red, 2014 vintage) made in 5 treatments: maceration of 7 days (control), 21 days and 49 days, and 21 and 49 days with seeds removed (85–90% of the seeds), 3 replicates each. Compares 49 days (seeds kept) and 49 days with seeds removed | 4.81 (49 days, seeds kept) | 3.56 (49 days, seeds removed) | mean bitterness (5-step QDA, 0 = not perceptible … 5 = strongly perceptible; higher is more bitter; 7 experts, 3 repetitions) | Condition named first (reference: no or short contact, seeds kept, low alcohol) more bitter Tested, significant |
| Direction shows which published value is larger. The Duncan test letters in Table 3 (the level is not stated in the excerpt; a separate test for each vintage) are a for 49 days with seeds and d for seeds removed. Astringency also fell, from 3.71 to 3.14.Removing the seeds compares the presence of seeds, not the length of contact, so this is a different finding from the rise in bitterness with longer contact Where: Results and discussion (sensory), Table 3 For whether changing only the length or method of contact with the skins and seeds (days of extraction, skin maceration, fermentation on the skins, removal of seeds) for the same grapes (or the same model wine liquid) changes the intensity of bitterness people perceive: Usable — A comparison of a method included in the question (seed removal): the same grapes, the same vintage and the same number of days with only 85–90% of the seeds removed, rated by the same 7 people. It is read as the effect of the presence of seeds, separately from the effect of the length of contact. The test is Duncan's letters, and how the 3 repetitions of the 7 people were treated cannot be read from the excerpt | |||||
| Bitterness intensity (sensory) | Seed removal: Plavac mali 2015 vintage: 49 days vs 49 days with seeds removed Plavac mali (red, 2015 vintage) made in 5 treatments: maceration of 7 days (control), 21 days and 49 days, and 21 and 49 days with seeds removed (85–90% of the seeds), 3 replicates each. Compares 49 days (seeds kept) and 49 days with seeds removed | 3.61 (49 days, seeds kept) | 3.49 (49 days, seeds removed) | mean bitterness (5-step QDA, 0 = not perceptible … 5 = strongly perceptible; higher is more bitter; 7 experts, 3 repetitions) | Condition named first (reference: no or short contact, seeds kept, low alcohol) more bitter Tested, significant |
| Direction shows which published value is larger. The Duncan test letters in Table 3 (the level is not stated in the excerpt; a separate test for each vintage) are a for 49 days with seeds and b for seeds removed. Astringency is 3.23 (ab) against 3.13 (bc), sharing a letter, so no difference was shown for astringency.Removing the seeds compares the presence of seeds, not the length of contact, so this is a different finding from the rise in bitterness with longer contact Where: Results and discussion (sensory), Table 3 For whether changing only the length or method of contact with the skins and seeds (days of extraction, skin maceration, fermentation on the skins, removal of seeds) for the same grapes (or the same model wine liquid) changes the intensity of bitterness people perceive: Usable — A comparison of a method included in the question (seed removal): the same grapes, the same vintage and the same number of days with only 85–90% of the seeds removed, rated by the same 7 people. It is read as the effect of the presence of seeds, separately from the effect of the length of contact. The test is Duncan's letters, and how the 3 repetitions of the 7 people were treated cannot be read from the excerpt | |||||
Orbanić 2023 sensory only
Applying Different Vinification Techniques in Teran Red Wine Production: Impact on Bioactive Compounds and Sensory Attributes. Foods 12(20):3838 — doi:10.3390/foods12203838
- How deeply checked
- Checked in full text — Full text via the Europe PMC XML (methods, sensory results and discussion, Table 1); Fig. 2 not viewed (the values for each treatment are in the figure only) Checked by: LLM (one extracted, another checked against the source; no human check), 2026-10-23.
- Samples
- Teran (red, Istria, Croatia). K7 (standard 7 days, control), C15 and C30 (crushed grapes cooled at 8 °C for 48 h before fermentation, then 13 or 28 days from the start of fermentation and maceration to the end of extended maceration; 15 or 30 days in total including the pre-treatment), H15 and H30 (heated at 50 °C for 48 h with the same extensions), CS15 (cooled, then saignée, extension 13 days); 3 replicates each, 18 wines
- Processing and cooking
- Not only the length of contact but also the temperature of the pre-treatment and the saignée differ
- How it was served or eaten
- 12 months after bottling; QDA on a 10-point structured scale (0 not perceptible, 10 strongly perceptible); the OIV 100-point method was also used in the same session
- Who rated, on what scale
- 7 accredited expert tasters (the panel of a laboratory accredited to ISO 17025); one-way ANOVA with Fisher's LSD (p ≤ 0.05)
| Measured | Comparison and condition | Condition named first (reference: no or short contact, seeds kept, low alcohol) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) | Unit | Direction / test |
|---|---|---|---|---|---|
| Bitterness intensity (sensory) | Teran (red): standard 7 days vs 5 treatments with a 48-hour pre-treatment and extended maceration (15 or 30 days in total) [values per treatment in a figure only] 6 treatments compared for bitterness by one-way ANOVA: K7 (standard 7 days), C15 and C30 (cooled at 8 °C for 48 hours, then 13 or 28 days from the start of fermentation and maceration to the end of extended maceration; 15 or 30 days in total including the pre-treatment), H15 and H30 (heated at 50 °C for 48 hours, then the same periods) and CS15 (cooled, then saignée, 13 days; 15 days in total) | The K7 value is in Fig. 2 only (Figure not obtained, so values unconfirmed) | The values of the 5 treatments are also in Fig. 2 only (Figure not obtained, so values unconfirmed); the range over all 6 treatments is 3.86–4.45 (text) | bitterness score (10-point structured scale, 0 = not perceptible … 10 = strongly perceptible; higher is more bitter; 7 experts) | Direction not given Tested, not significant |
| The text says the bitterness of Teran was statistically equal across all treatments (the source's wording). The values per treatment are in Fig. 2 only, there is no p value for this pair and no direction is read. Not only the length of contact but also the temperature of the pre-treatment and the saignée differ. The 13 and 28 days run from the start of fermentation and maceration to the end of extended maceration, not from the end of fermentation (methods 2.3, Table 1). Astringency is 3.95–5.50 (text; whether it differs is not stated). A co-author, Jeromel, is shared with Jagatić Korenika 2023 Where: Methods 2.3, Table 1; results and discussion (sensory analysis), Fig. 2; text For whether changing only the length or method of contact with the skins and seeds (days of extraction, skin maceration, fermentation on the skins, removal of seeds) for the same grapes (or the same model wine liquid) changes the intensity of bitterness people perceive: Limited — Not only the length of contact but also the temperature of the pre-treatment and the saignée differ, the values per treatment are in a figure only, and the values and test for a pair that differs only in the length of contact cannot be read | |||||
Blackford 2026 sensory only
Oenological Characterization of Divona, a New Disease-Resistant Variety, and Preliminary Insights into the Influence of Maceration and Fermentation Temperature Across Three Vintages. Foods 15(19):3358 — doi:10.3390/foods15193358
- How deeply checked
- Checked in full text — Full text via the Europe PMC XML (methods, Table 3, discussion) Checked by: LLM (one extracted, another checked against the source; no human check), 2026-10-23.
- Samples
- Divona (disease-resistant white, Pully, Vaud, Switzerland, vintages 2019, 2020 and 2022). Direct pressing versus 12 hours of pre-fermentation maceration at 12 °C after crushing, fermentation at 15 °C and 20 °C; 4 tanks per year (12 in all), so no technical replicates
- Processing and cooking
- Not applicable (only pre-fermentation maceration and fermentation temperature were varied)
- How it was served or eaten
- 3 months after bottling at 17 ± 1 °C, 50 mL; each wine rated twice on the same day on a line scale from 1 (no perception) to 7 (very intense)
- Who rated, on what scale
- 12 experienced tasters trained every year; 14 attributes; linear mixed model with p values adjusted for multiple testing (BH)
| Measured | Comparison and condition | Condition named first (reference: no or short contact, seeds kept, low alcohol) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) | Unit | Direction / test |
|---|---|---|---|---|---|
| Bitterness intensity (sensory) | Divona (white): direct pressing vs 12 hours of pre-fermentation maceration at 12 °C [no mean per group, no technical replicates] Divona from 3 vintages (2019, 2020 and 2022) compared with direct pressing and with 12 hours of pre-fermentation maceration at 12 °C after crushing (linear mixed model over fermentation temperatures of 15 °C and 20 °C) | Not given (the mean for direct pressing is not in the source; the overall mean is 2.4 ± 0.8) | Not given (the mean for pre-fermentation maceration is not in the source) | bitterness score (line scale from 1 = no perception to 7 = very intense; higher is more bitter; 12 experienced tasters, 2 ratings) | Direction not given Tested, not significant |
| The effect of maceration is p=0.912 (after BH adjustment), of fermentation temperature p=0.973 and of the interaction p=0.157. No significant effect of maceration was shown for any of the 14 attributes. The authors write that non-significance does not mean there is no effect and reflects limited statistical power from the lack of technical replicates. The effect of vintage is large. There are 12 tanks (3 years × 2 × 2), and bitterness was tested in the model without the tank effect Where: Results (sensory analysis), Table 3; discussion For whether changing only the length or method of contact with the skins and seeds (days of extraction, skin maceration, fermentation on the skins, removal of seeds) for the same grapes (or the same model wine liquid) changes the intensity of bitterness people perceive: Limited — The same grapes were macerated before fermentation or not, but there is no mean per group and there are no technical replicates | |||||
Magrini 2016 sensory only
On prefermentative maceration techniques: statistical analysis of sensory descriptors in Sangiovese wine. Biom Lett 53(1):1-20 — doi:10.1515/bile-2016-0001
- How deeply checked
- Checked in full text — Full text via the publisher's Sciendo PDF (methods and results); the estimates in the appendix were not viewed Checked by: LLM (one extracted, another checked against the source; no human check), 2026-10-23.
- Samples
- Sangiovese (red, 2008 vintage, south Tuscany). Standard fermentation (CTRL), cold soak (5 °C for 48 hours, CSPF) and cryomaceration (liquid nitrogen, CRYO), crossed with fermentation temperature of 20 or 30 °C and with saignée or not; 3 replicates, 36 fermentations; maceration lasted 14 days in all treatments
- Processing and cooking
- Not applicable (the pre-fermentation treatment was varied)
- How it was served or eaten
- 12 months after bottling; bitterness was rated after expelling the wine from the mouth; each descriptor on a 4-level scale
- Who rated, on what scale
- 15 people involved in the experiment (wine experts, winemakers and 1 non-expert); 6 training sessions; cumulative link mixed model; because the panel was made up of people involved in the experiment, a conflict of interest is possible
| Measured | Comparison and condition | Condition named first (reference: no or short contact, seeds kept, low alcohol) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) | Unit | Direction / test |
|---|---|---|---|---|---|
| Bitterness rating (the scale steps and their direction cannot be confirmed in the source) | Sangiovese (red): standard fermentation vs cold soak for 48 hours or cryomaceration [no values] A trial with 3 replicates in which standard fermentation (CTRL), cold soak at 5 °C for 48 hours (CSPF) and cryomaceration with liquid nitrogen (CRYO) were crossed with fermentation temperatures of 20 and 30 °C and with saignée or not; cumulative link mixed model | Not given (no values are shown) | Not given (no values are shown) | bitterness rating (4 levels; the source calls it a hedonistic scale, and the definition of the levels and which end is higher are unconfirmed, so it is not confirmed to be an intensity scale; 15 people involved in the experiment) | Direction not given Tested, not significant |
| The text says bitterness was not significantly affected by any experimental factor. Only the attributes that were significant (colour, aromas, volume, tannic intensity, astringency and dryness) are tabulated, and no values or pairwise p values for bitterness are shown. Maceration lasted 14 days in all treatments. The panel was people involved in the experiment (wine experts, winemakers and 1 non-expert), so a conflict of interest is possible Where: Results (start of the section), Table 3 For whether changing only the length or method of contact with the skins and seeds (days of extraction, skin maceration, fermentation on the skins, removal of seeds) for the same grapes (or the same model wine liquid) changes the intensity of bitterness people perceive: Limited — The same grapes were given different pre-fermentation treatments, but there are no values and the panel was people involved in the experiment, so a conflict of interest is possible | |||||
Stoffel 2025 sensory only
The Chemical and Sensory Impact of Cap Management Techniques, Maceration Length, and Ethanol Level in Syrah Wines from the Central Coast of California. Molecules 30(8):1694 — doi:10.3390/molecules30081694
- How deeply checked
- Checked in full text — Full text via the Europe PMC XML (methods, results and discussion of the modified Pivot Profile); supplementary figures and tables not viewed Checked by: LLM (one extracted, another checked against the source; no human check), 2026-10-23.
- Samples
- Syrah (red, 2022 vintage, California). Punch down twice daily (control), submerged cap, and extended maceration (half of the punch-down control tanks left on the skins for up to 6 months, rated at 3 months), each with 2 ethanol levels (chaptalised or not); 3 replicates each
- Processing and cooking
- Not applicable (cap management and the length of maceration were varied)
- How it was served or eaten
- Modified Pivot Profile: free responses were replaced by a multiple-choice questionnaire of attributes chosen in advance (each attribute answered as "less than" or "more than" the reference, the Pivot) (text 4.3.1); the reference is PD_Nat (punch down, not chaptalised); the text and a supplementary figure legend say the sensory analysis took place at the 3-month point of extended maceration
- Who rated, on what scale
- 15 winemakers (an expert panel, trained for 2 hours on the day of evaluation in the procedure and the attributes and reference standards chosen in advance); Fisher's exact test (p < 0.05)
| Measured | Comparison and condition | Condition named first (reference: no or short contact, seeds kept, low alcohol) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) | Unit | Direction / test |
|---|---|---|---|---|---|
| Answers on whether bitterness was more or less than a reference sample (sensory; not an intensity score) | Syrah (red): reference (punch down, not chaptalised) vs extended maceration (rated at 3 months) [no individual result for bitterness; answers relative to a reference] With the punch-down (2 times a day), non-chaptalised wine (PD_Nat) as the reference (the Pivot), extended maceration (EM; half of the punch-down control tanks left for up to 6 months, rated at 3 months) without chaptalisation (EM_Nat) and with chaptalisation (EM_Chap) was compared with the reference in a modified Pivot Profile | Not given (the reference wine PD_Nat; it is the reference and is not itself rated) | Not given (the numbers of bitterness answers for EM_Nat and EM_Chap are not shown) | choice of whether bitterness was "less than" or "more than" the reference (a multiple-choice questionnaire of attributes chosen in advance; 15 winemakers, with a 2-hour training on the procedure and attributes on the day of evaluation) | Direction not given Test method described; result for this comparison not reported |
| In the correspondence analysis the extended-maceration wines lay near bitterness (Fig. 1). The text says the only taste or mouthfeel attribute significant by Fisher's exact test (p < 0.05) was the astringency sub-quality "satin", and Table 5 shows only significant attributes, so the numbers of bitterness answers and the p value are not shown. The test label is therefore "no result reported", not "not significant". The reference is PD_Nat (punch down, not chaptalised), so comparing EM_Nat with the reference amounts to comparing extended maceration with punch down at the same (no) chaptalisation. EM_Chap also differs in chaptalisation. The method replaced free responses with a questionnaire for choosing attributes selected in advance (text 4.3.1). The text says Fisher's exact test compared the observed value of each wine with the expected value in a contingency table to decide whether it was less or more than the reference. The sensory analysis was done at the 3-month point of extended maceration, while the wines were left on the skins for up to 6 months (text 4.3.2 and supplementary figure legend) Where: Results and discussion 2.4 (modified Pivot Profile), Fig. 1 and Table 5; methods 4.3.1, 4.3.2 and 4.4 For whether changing only the length or method of contact with the skins and seeds (days of extraction, skin maceration, fermentation on the skins, removal of seeds) for the same grapes (or the same model wine liquid) changes the intensity of bitterness people perceive: Limited — Each wine is compared with a reference (punch down, not chaptalised), so comparing EM_Nat with the reference amounts to comparing extended maceration with punch down at the same (no) chaptalisation, but the numbers of bitterness answers and the test result are not shown; EM_Chap also differs in chaptalisation | |||||
Iino 2004 sensory only
白ワインにおいて後味として強く残るカプリル酸エチルの苦味について (Strong Bitterness of Ethyl Caprylate as An Unpleasant Aftertaste of White Wines). 醸協 99(4):281-288（Journal of the Brewing Society of Japan） — doi:10.6013/jbrewsocjapan1988.99.281
- How deeply checked
- Checked in full text — Full text via the J-STAGE PDF (text and Tables 1–7 checked as images); the 1994 study by Iino and Watanabe from the same centre is not a comparison of conditions and is not a row Checked by: LLM (one extracted, another checked against the source; no human check), 2026-10-23.
- Samples
- 200 kg of Koshu (white) grapes were divided into 28 kg lots and fermented either with skins and seeds (skin-contact fermentation after crushing and destemming, 3 days at 25 °C = M-25 or 5 days at 15 °C = M-15, stirred morning and evening, then pressed) or as juice (pressed at once after crushing, J-25 and J-15); a separate set of tests used ethyl caprylate and other esters in ethanol solutions
- Processing and cooking
- Not applicable (skin-contact fermentation versus none); alcohol also differs (Table 1)
- How it was served or eaten
- For the wines, whether a strong lingering bitter aftertaste was pointed out (yes or no); there is no intensity score; the ethanol solution tests had 9, 14 and 20 people point it out in the same way
- Who rated, on what scale
- For the wines, 5 expert panellists (3 staff of the centre and 2 from wineries in the prefecture); the ethanol solution tests drew on 20 people from the centre and 11 wineries; a one-sided test of the number of people pointing it out (stated as chi-square with 1 degree of freedom); no test for the comparison of the wines
| Measured | Comparison and condition | Condition named first (reference: no or short contact, seeds kept, low alcohol) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) | Unit | Direction / test |
|---|---|---|---|---|---|
| Whether bitterness was noted (description; not a count or an intensity score) | Koshu (white): fermentation as juice vs skin-contact fermentation (3 days at 25 °C or 5 days at 15 °C) [yes or no only, no numbers of people, 5 people, no test; no direction label (no numbers)] 200 kg of Koshu grapes divided into 28 kg lots: juice fermentation pressed at once after crushing (J-25 and J-15) versus skin-contact fermentation mixed with the skins and seeds for 3 days at 25 °C (M-25) or 5 days at 15 °C (M-15) | Juice fermentation (J-25 and J-15): "bitterness as aftertaste" in the taste column of Table 2 | Skin-contact fermentation (M-25 and M-15): "—" in the taste column of Table 2 | whether a bitter aftertaste was pointed out (the entry in the taste column of Table 2; 5 expert panellists; the number of people who pointed it out and an intensity score are not shown) | Direction not given No test reported |
| There are no published values (numbers of people or scores) whose sizes could be compared, so no direction label is given. The taste column of Table 2 gives "bitterness as aftertaste" for juice fermentation and "—" for skin-contact fermentation. The text says skin-contact fermented white wine has less of a strong lingering bitter aftertaste and cites earlier reports from the Yamanashi prefectural centre. There is no test and no breakdown of numbers. Other differences at the same time (Table 1): alcohol is 9.8% for M-25 and 11.6% for J-25 (10.6% for M-15 and J-15), total acidity 5.9 g/L for M-15 and 7.4 for J-15, pH 3.30 for skin-contact and 3.22–3.23 for juice. Total phenols are higher in skin-contact fermentation (M-25 1077, J-25 538, M-15 690, J-15 515 mg/L). Ethyl caprylate is 0.4 and 0.5 mg/L in skin-contact fermentation and 1.1 and 1.4 in juice fermentation (Table 3), and the authors say isoamyl alcohol showed no difference. This is not proof of a cause Where: Results 1, Tables 1–3 For whether changing only the length or method of contact with the skins and seeds (days of extraction, skin maceration, fermentation on the skins, removal of seeds) for the same grapes (or the same model wine liquid) changes the intensity of bitterness people perceive: Limited — The same grapes were fermented with or without skin contact, but the rating was whether 5 people pointed out bitterness, there is no test, and alcohol, total acidity and pH also differ | |||||
| Number of panellists who noted bitterness (sensory; not an intensity score) | Substance threshold (ethanol solution): ethyl caprylate 0 vs 0.75 mg/L (ethanol 8%) [difference in ethyl caprylate concentration; not a comparison of contact] 8% ethanol solutions with ethyl caproate at 1 mg/L (added to all to mask aroma) and ethyl caprylate, with 14 people indicating whether they perceived a strong lingering bitter aftertaste; ethyl caprylate at 0 (control) and 0.75 mg/L | 0 people (0 mg/L) | 11 people (0.75 mg/L, of 14) | number of people pointing out a strong lingering bitter aftertaste (of 14; higher means more people found it bitter) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) higher Test method described; result for this comparison not reported |
| Direction shows which published number of people is larger. What was measured is the number of people who pointed out bitterness, not bitterness intensity. The methods say the presence or absence of bitterness was judged for each sample by a chi-square test with 1 degree of freedom, and the marks in Table 5 are judgements for the sample at each concentration (* for 0.75 mg/L, one-sided 5%). No result of a test of the pair 0 mg/L against 0.75 mg/L is given, so the test label is "no result reported". 0.25 mg/L has 3 people, 0.5 mg/L has 7, 1.0 mg/L has 13 (**, 1%) and 1.5 mg/L has 14 (***, 0.1%). In a separate Table 4 (3 esters at 1.5 mg/L each, 9 people), ethyl caprylate has 8 people (*, one-sided 5%), ethyl caproate 2 and ethyl caprate 3, but the text gives 3 and 2 for caproate and caprate the other way round, so the table and the text disagree. This is a test of a substance and does not prove that it causes the difference in bitterness between skin-contact and juice fermentation (the authors read it as the component, among those that differed, that was bitter in the sensory test). Among 39 dry white wines entered in the Yamanashi wine competition, the mean ethyl caprylate is 1.2 ppm for 16 new Koshu wines and 1.3 ppm for 11 aged Koshu wines (text; not the mean of all 39) Where: Methods 3; results 2-2 and 3; Table 5 For whether changing only the length or method of contact with the skins and seeds (days of extraction, skin maceration, fermentation on the skins, removal of seeds) for the same grapes (or the same model wine liquid) changes the intensity of bitterness people perceive: Not usable — A test of a substance in ethanol solutions, not wine, without changing contact with the skins and seeds, so it cannot be used for the comparison of contact; shown as material for thinking about the difference between skin-contact and juice fermentation (not proof of a cause) | |||||
| Number of panellists who noted bitterness (sensory; not an intensity score) | Substance threshold (ethanol solution): ethanol 4% vs 8% (ethyl caprylate 2 mg/L) [difference in ethanol concentration; not a comparison of contact] Ethanol solutions containing ethyl caprylate at 2 mg/L and ethyl caproate at 1 mg/L at ethanol concentrations of 4, 6, 8, 10 and 12%, with 20 people indicating whether they perceived a strong lingering bitter aftertaste; 4% is compared with 8% | 0 people (4%) | 15 people (8%, of 20) | number of people pointing out a strong lingering bitter aftertaste (of 20; higher means more people found it bitter) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) higher Test method described; result for this comparison not reported |
| Direction shows which published number of people is larger. What was measured is the number of people who pointed out bitterness, not bitterness intensity. The methods say the presence or absence of bitterness was judged for each sample by a chi-square test with 1 degree of freedom, and the marks in Table 6 are judgements for the sample at each concentration (* for 8%, one-sided 5%). No result of a test of the pair 4% against 8% is given, so the test label is "no result reported". 6% has 4 people, 10% has 19 (***, 0.1%) and 12% has 20 (***, 0.1%). This is a test of the combination of ethanol concentration and a substance, not of conditions of contact with the skins of a wine (a separate frame for substance thresholds) Where: Methods 3; results 2-3; Table 6 For whether changing only the length or method of contact with the skins and seeds (days of extraction, skin maceration, fermentation on the skins, removal of seeds) for the same grapes (or the same model wine liquid) changes the intensity of bitterness people perceive: Not usable — A test of a substance in ethanol solutions, not wine, without changing contact with the skins and seeds, so it cannot be used for the comparison of contact; shown as material for thinking about the difference between skin-contact and juice fermentation (not proof of a cause) | |||||
Sancho-Galán 2021 sensory only
Influence of the Presence of Grape Skins during White Wine Alcoholic Fermentation. Agronomy 11(3):452 — doi:10.3390/agronomy11030452
- How deeply checked
- Checked in full text — Methods and results of the MDPI page read in the built-in browser and checked against the saved excerpt; the image of Fig. 4 (radar chart) was also viewed, but its values are too rough to put in the table Checked by: LLM (one extracted, another checked against the source; no human check), 2026-10-23.
- Samples
- Palomino Fino (white). Skins added during fermentation at 0 (control), 20, 40, 60, 80 and 100% by volume of the must; duplicate 5 L fermentations at 18 °C for 21 days
- Processing and cooking
- Not applicable (the proportion of skins added during fermentation was varied)
- How it was served or eaten
- 5 days after bottling; 10-point scale; bitterness is in the radar chart of Fig. 4 and the text gives only a correlation; the legend of the figure says visual and olfactory, which does not match the text
- Who rated, on what scale
- 20 experienced people; two-way ANOVA with Bonferroni correction
| Measured | Comparison and condition | Condition named first (reference: no or short contact, seeds kept, low alcohol) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) | Unit | Direction / test |
|---|---|---|---|---|---|
| Bitterness intensity (sensory) | Palomino Fino (white): skins added during fermentation at 0% vs 100% [values in a figure only; no direction label (values not checked); no test result for bitterness in this pair] Skins added during fermentation of Palomino Fino (white) at 0 (control) to 100% of the must by volume (2 replicate 5 L fermentations, 18 °C, 21 days), rated by 20 experienced people on a 10-point scale 5 days after bottling; 0% is compared with 100% | Only a rough visual reading of the figure, so not used (the text says the control was lowest) | Only a rough visual reading of the figure, so not used (the text says 100% was highest) | bitterness score (10-point scale; higher is more bitter; 20 experienced people; values are in the radar chart of Fig. 4 only) | Direction not given Test method described; result for this comparison not reported |
| The values are only in the radar chart of Fig. 4 and a visual reading would be rough, so they are not read; since their sizes cannot be compared, no direction label is given. The text says bitterness correlated positively with the proportion of skins (r=0.9724), lowest in the control and highest at 100%. The methods give a two-way ANOVA with Bonferroni multiple comparisons, but the text gives no result of a test of bitterness between 0% and 100%, so the test label is "no result reported". The bitterness axis of Fig. 4 carries a **** mark, but which pair it tests cannot be read. The legend says visual and olfactory, which does not match the text treating taste attributes as values in Fig. 4. What was read is a saved browser excerpt; a check against the source page reopened remains Where: Methods (sensory analysis, statistics); results (sensory analysis), Fig. 4; text For whether changing only the length or method of contact with the skins and seeds (days of extraction, skin maceration, fermentation on the skins, removal of seeds) for the same grapes (or the same model wine liquid) changes the intensity of bitterness people perceive: Limited — The same grapes had different proportions of skins, but the text gives no test result for bitterness in this pair, and the values are in a figure only and rough | |||||
Philipp 2024 sensory only
The Influence of Prefermentation Skin Contact, Stabulation, and Skin Fermentation on the Aromatic Behaviour and Phenolic Compounds of Important Austrian White Wine Cultivars. Aust J Grape Wine Res 2024:1-22 — doi:10.1155/2024/9843225
- How deeply checked
- Checked in full text — Main text of the Wiley page read in the built-in browser and checked against the saved excerpt; the number of mentions of bitterness is only in a supplementary table, which was not obtained Checked by: LLM (one extracted, another checked against the source; no human check), 2026-10-23.
- Samples
- Grüner Veltliner (white). C (direct pressing), SC 12 hours (skin contact at 15 °C), PMF (partial fermentation on the skins, the skins removed when fermentation was half complete) and FMF (fermentation on the skins for the whole period), at 15 °C and 25 °C; 3 replicates each; also Pinot Blanc, Sauvignon Blanc and Traminer with skin contact of 12 and 24 hours
- Processing and cooking
- Not applicable (the length and method of contact with the skins were varied)
- How it was served or eaten
- CATA (check all that apply); the 3 replicates were pooled into 1 sample for evaluation
- Who rated, on what scale
- 24 experts; the text says this design does not allow statistical testing
| Measured | Comparison and condition | Condition named first (reference: no or short contact, seeds kept, low alcohol) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) | Unit | Direction / test |
|---|---|---|---|---|---|
| Number of times bitterness was ticked or mentioned (e.g. check-all-that-apply; not an intensity score) | Grüner Veltliner (white): direct pressing vs fermentation on the skins [no test, 1 pooled CATA sample; no direction label (numbers of mentions not obtained)] Direct pressing (C) and fermentation on the skins (PMF and FMF; 15 °C and 25 °C) of Grüner Veltliner (white), compared by 24 experts in CATA (the 3 replicates pooled into 1 sample) | The number of mentions of bitterness is in a supplementary table only (supplementary table not obtained, so values unconfirmed) | The number of mentions of bitterness is in a supplementary table only (supplementary table not obtained, so values unconfirmed) | number of times bitterness was ticked (CATA, check all that apply; 24 experts) | Direction not given No test reported |
| The numbers of mentions are only in supplementary tables S11–S14, which were not obtained, so their sizes cannot be compared and no direction label is given. The text says the wines fermented on the skins were described as bitter, and the abstract says bitterness increased. The text says this experimental design does not allow statistical testing. The text says catechins, taken as an indicator of bitterness in white wine, showed no significant difference by treatment. No test result supporting the abstract's statement that bitterness increased was found in what was read Where: Results and discussion (sensory); abstract For whether changing only the length or method of contact with the skins and seeds (days of extraction, skin maceration, fermentation on the skins, removal of seeds) for the same grapes (or the same model wine liquid) changes the intensity of bitterness people perceive: Limited — The design does not allow testing (the 3 replicates pooled into 1 sample), and the numbers of mentions of bitterness are in a supplementary table only (not obtained) | |||||
Yuan 2025 sensory only
Effects of Prolonged Pomace Contact on Color and Mouthfeel Characteristics in Merlot Wine During the Ageing Process Under Microwave Irradiation. Foods 14(3):507 — doi:10.3390/foods14030507
- How deeply checked
- Checked in full text — Full text via the Europe PMC XML (methods, sensory results and discussion); only a challenge-page HTML could be obtained for the sensory radar chart (Fig. 4b), so it was not viewed Checked by: LLM (one extracted, another checked against the source; no human check), 2026-10-23.
- Samples
- Merlot (red, 2022 vintage, about 50 kg). 2 storage strategies, either the skins and seeds filtered off after fermentation (no pomace) or the pomace left in prolonged contact, crossed with microwave treatment (500 W, 40 °C, daily for 15 days, 4 durations): 8 treatments, 3 replicates each; sensory evaluation after 120 days of storage
- Processing and cooking
- Microwave treatment is crossed with the length of contact with the pomace
- How it was served or eaten
- Room temperature (20 ± 2 °C) in random order; 8 attributes (quality, alcohol, colour, clarity, bitterness, astringency, persistence, mouthfeel) on a 10 cm line scale (0 no sensation, 10 extremely high)
- Who rated, on what scale
- 10 trained assessors; no test of the sensory results (radar chart only)
| Measured | Comparison and condition | Condition named first (reference: no or short contact, seeds kept, low alcohol) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) | Unit | Direction / test |
|---|---|---|---|---|---|
| Bitterness intensity (sensory) | Merlot (red): stored without pomace vs stored with prolonged pomace contact [the direction for pomace contact alone cannot be read; crossed with microwave treatment; no test; values in a figure only] Merlot (2022 vintage) stored in 2 ways, either with the skins and seeds filtered off after fermentation (no pomace) or with the pomace left in prolonged contact, crossed with 4 microwave treatment levels, 8 treatments in all, evaluated after 120 days of storage | In the radar chart of Fig. 4b only (Figure not obtained, so values unconfirmed) | In the radar chart of Fig. 4b only (Figure not obtained, so values unconfirmed) | bitterness score (10 cm line scale, 0 = no sensation … 10 = extremely high; higher is more bitter; 10 trained assessors) | Direction not given No test reported |
| No direction is read for pomace contact alone. Methods 2.2 describe a two-factor design crossing the presence of pomace (no pomace or prolonged pomace contact) with 4 levels of microwave treatment, and in the sensory paragraph (3.6) the subject that lowered bitterness is the microwave treatment. The conclusions say that with prolonged pomace contact clarity and yellowness rose and bitterness and astringency fell with lower total phenols, total tannins and flavan-3-ols, but this is a conclusion of a trial combined with microwave treatment, and the direction when only pomace contact changes at the same microwave condition cannot be taken from the text. Fig. 4b was not obtained, so values are unconfirmed. There is no test of the sensory results. The scores of the 8 attributes range from 2.8 to 8.7 (text). Results 3.3 say that prolonged pomace contact had no positive effect on bitterness and astringency, because flavan-3-ols were significantly lower in wines with prolonged pomace contact than without pomace (an inference from composition, not a sensory comparison) Where: Methods 2.2; results and discussion 3.3 and 3.6 (sensory), Fig. 4b; conclusions For whether changing only the length or method of contact with the skins and seeds (days of extraction, skin maceration, fermentation on the skins, removal of seeds) for the same grapes (or the same model wine liquid) changes the intensity of bitterness people perceive: Limited — A design crossing the presence of pomace with microwave treatment, so the direction for pomace contact alone cannot be taken from the text; there is no test of the sensory results, and the values are in a figure only (not obtained) | |||||
Sokolowsky 2015 sensory only
Sensory impact of skin contact on white wines characterized by descriptive analysis, time-intensity analysis and temporal dominance of sensations analysis. Food Quality and Preference — doi:10.1016/j.foodqual.2014.07.002
- How deeply checked
- Abstract only — Abstract only (the full text is behind a paywall); the abstract was reread via Europe PMC this time; values, numbers of people and pairwise tests are not in the abstract Checked by: LLM (one extracted, another checked against the source; no human check), 2026-10-23.
- Samples
- Riesling and Gewürztraminer (white, 2009 and 2010 vintages) made with different skin contact times, including a wine fermented completely on the skins
- Processing and cooking
- Not applicable (skin contact time was varied)
- How it was served or eaten
- Three methods: descriptive analysis (DA), time-intensity analysis (TI) and temporal dominance of sensations (TDS); details are not in the abstract
- Who rated, on what scale
- Not given (the abstract gives no number of people, scale or test method)
| Measured | Comparison and condition | Condition named first (reference: no or short contact, seeds kept, low alcohol) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) | Unit | Direction / test |
|---|---|---|---|---|---|
| Bitterness intensity (sensory) | Riesling and Gewürztraminer (white): wines made with different skin contact times [abstract only, no values; no direction label (no values)] Riesling and Gewürztraminer (2009 and 2010 vintages) made with different skin contact times (including a wine fermented completely on the skins) and evaluated by descriptive analysis (DA), time-intensity analysis (TI) and temporal dominance of sensations (TDS) | Not given (no values in the abstract) | Not given (no values in the abstract) | Not given (no scale or number of people in the abstract) | Direction not given Tested, significant |
| The abstract only; there are no values whose sizes could be compared, so no direction label is given. The wine fermented completely on the skins was significantly more bitter than all other wines by time-intensity analysis (TI) and descriptive analysis (DA), whereas by temporal dominance of sensations (TDS) the dominant sensation was not bitterness but the astringent mouthfeel. Taken method by method, in DA Riesling differed significantly only in bitterness and colour, and Gewürztraminer in bitterness, sweetness, sourness, astringency and others; the TI bitterness curves of Gewürztraminer differed significantly in maximum intensity and area under the curve, while Riesling showed no significant difference in any TI parameter. Which variety the wine fermented completely on the skins was cannot be read from the abstract. Methods, numbers of people and pairwise tests are not in the abstract, so the details of the tests are unconfirmed Where: Abstract (Europe PMC) For whether changing only the length or method of contact with the skins and seeds (days of extraction, skin maceration, fermentation on the skins, removal of seeds) for the same grapes (or the same model wine liquid) changes the intensity of bitterness people perceive: Limited — The same grapes had different skin contact times, but only the abstract was read, so values, numbers of people and pairwise tests cannot be checked | |||||
Fontoin 2008 sensory only
Effect of pH, ethanol and acidity on astringency and bitterness of grape seed tannin oligomers in model wine solution. Food Quality and Preference — doi:10.1016/j.foodqual.2007.08.004
- How deeply checked
- Abstract only — Abstract only (the full text is behind a paywall); the abstract was reread via Europe PMC this time; no values are in the abstract Checked by: LLM (one extracted, another checked against the source; no human check), 2026-10-23.
- Samples
- A model wine solution containing oligomeric tannins from grape seeds, varying pH, ethanol and tartaric acid concentration one at a time (a solution, not a wine)
- Processing and cooking
- Not applicable (the composition of the solution was varied, not the conditions of contact with skins and seeds)
- How it was served or eaten
- Bitterness and overall astringency intensities rated in succession (abstract); details are not in the abstract
- Who rated, on what scale
- 16 judges (abstract); the scale and test method are not in the abstract
| Measured | Comparison and condition | Condition named first (reference: no or short contact, seeds kept, low alcohol) | Condition named second (longer contact, fermentation on the skins, seeds removed, high alcohol) | Unit | Direction / test |
|---|---|---|---|---|---|
| Bitterness intensity (sensory) | Alcohol (not a contact variable): varying ethanol in a model wine solution (including 11–15%) [abstract only, no values, a solution and not wine] In a model wine solution with oligomeric tannins from grape seeds, pH, ethanol and tartaric acid concentration were varied one at a time and 16 judges rated bitterness and astringency | Not given (no values in the abstract) | Not given (no values in the abstract) | Not given (no scale in the abstract; 16 judges) | Direction not given No test reported |
| The abstract only. Ethanol contributed to perceived bitterness as well (especially at typical wine levels of 11–15%), pH affected only astringency, and changing tartaric acid concentration at constant pH affected neither. The direction (whether bitterness rises with ethanol), the values and the test method are not in the abstract, so no direction is read. This is not a comparison of contact with skins and seeds and is shown as a reference for the ethanol, pH and acidity axis Where: Abstract (Europe PMC) For whether changing only the length or method of contact with the skins and seeds (days of extraction, skin maceration, fermentation on the skins, removal of seeds) for the same grapes (or the same model wine liquid) changes the intensity of bitterness people perceive: Not usable — A test that varied ethanol and other factors in a model solution, not wine, without changing contact with the skins and seeds, so it cannot be used for the comparison of contact; only the abstract was read, so no direction can be read; shown as material for thinking about the effect of alcohol | |||||
What was established within an experiment
Only results observed in comparisons within one study. Results with no test shown are stated as such.
- In Lisjak 2020, for the extract of seeds soaked in the model wine liquid with 12% ethanol and pH 3.2, the rank sums of bitterness were 11 for 3 days and 10 for 5 days against 24 for 15 days and 27 for 20 days, and 15 and 20 days were significantly higher than 3 and 5 days (LSD 5%). For the skin extract the text says there was no significant difference by days, but the letters in the table differ between 5 and 7 days for bitterness, with similar disagreements for astringency and colour, and the cause is not given in the source. [rows: Lisjak 2020 Seed extract in the model wine liquid: 3 days vs 20 days of extraction; Lisjak 2020 Seed extract in the model wine liquid: 5 days vs 20 days of extraction; Lisjak 2020 Skin extract in the model wine liquid: 3 days vs 20 days of extraction [text and table letters disagree]]
- In the fermenting Cabernet (Lisjak 2020, 3 tanks of 7 tonnes), the rank sums of bitterness were 7 on day 3 and 10 on day 5 against 30 on day 11, 32 on day 13 and 30 on day 15, and days 3 and 5 were significantly lower than days 11, 13 and 15. Over the same period ethanol rose from 0.6% to 14.2%, and the authors write that perceived bitterness in fermenting wine may also depend on changes in alcohol and sugar. The extraction in the model liquid was set up to avoid this. [rows: Lisjak 2020 Wine during fermentation: day 3 vs day 15 [ethanol also rises with fermentation]; Lisjak 2020 Wine during fermentation: day 5 vs day 15 [ethanol also rises with fermentation]]
- In Chenin Blanc (Aleixandre-Tudo 2015), the wine fermented on the skins for the whole fermentation was rated more bitter than the control (46.70 against 30.36) and also higher in astringency (41.33 against 25.76) and sourness. At the same time pH was lower, 3.34 against 3.39, total acidity higher, 6.23 against 5.52, and fructose lower, 1.77 against 7.92. Ethanol showed no significant difference across the 3 groups (15.74, 15.76 and 16.06%, p=0.325). The skin contact of 12 hours at 4 °C before fermentation had the same letter as the control (31.16 against 30.36). [rows: Aleixandre-Tudo 2015 Fermentation on the skins for the whole fermentation: control vs FoS [other differences besides the skins]; Aleixandre-Tudo 2015 Contact with the skins before fermentation (4 °C, 12 hours): control vs ScBF]
- In the Cabernet Sauvignon of Pazos 2026, 8 months of extended maceration was higher in bitterness than 10 days on the skins (46.83 against 37.61, p<0.0001), and the difference in astringency was larger still (63.72 against 35.31). A main effect of alcohol also appeared separately: 35.55 for low (about 10.5%) against 47.13 for high (about 16.5%), while medium (about 13.5%) at 43.97 had the same letter as high and no difference was shown. The maceration × alcohol interaction was p=0.8157 and not shown, but harvest × alcohol was p=0.0018, and the means for alcohol average over it. [rows: Pazos 2026 Maceration: control (10 days on the skins) vs extended (8 months) [main effect]; Pazos 2026 Alcohol (not a contact variable): low (about 10.5%) vs high (about 16.5%) [main effect]; Pazos 2026 Alcohol (not a contact variable): medium (about 13.5%) vs high (about 16.5%) [main effect]]
- For the 2014 vintage of Plavac mali (Jagatić Korenika 2023), the bitterness scores were 4.23 for 7 days, 4.33 for 21 days and 4.81 for 49 days, with the same letter for 7 and 21 days and a different one for 49 days only. The 2015 vintage had smaller differences, 3.54, 3.57 and 3.61, and on the 5-step scale the letters differed between 7 and 49 days. In the 2014 vintage astringency went down with longer maceration, the opposite of bitterness (3.95 against 3.71). With the seeds removed, both bitterness and astringency fell in the 2014 vintage. At 49 days in the 2015 vintage, bitterness was lower without seeds, but astringency shared a letter and no difference was shown. [rows: Jagatić Korenika 2023 Plavac mali 2014 vintage: maceration of 7 days vs 49 days; Jagatić Korenika 2023 Plavac mali 2014 vintage: maceration of 7 days vs 21 days; Jagatić Korenika 2023 Plavac mali 2015 vintage: maceration of 7 days vs 49 days [the difference is a small 0.07]; Jagatić Korenika 2023 Plavac mali 2015 vintage: maceration of 7 days vs 21 days; Jagatić Korenika 2023 Seed removal: Plavac mali 2014 vintage: 21 days vs 21 days with seeds removed; Jagatić Korenika 2023 Seed removal: Plavac mali 2014 vintage: 49 days vs 49 days with seeds removed; Jagatić Korenika 2023 Seed removal: Plavac mali 2015 vintage: 49 days vs 49 days with seeds removed]
- Reports whose values or tests could not be checked are lined up in the table with a test label. Sancho-Galán 2021 writes that bitterness correlated positively (r=0.9724) with the proportion of skins added during fermentation, but, although statistical methods are described, the result of a test of bitterness between 0% and 100% cannot be confirmed. In Philipp 2024 the wines fermented on the skins were described as bitter, but the design did not allow testing. Sokolowsky 2015 (abstract only) writes that the wine fermented completely on the skins was significantly more bitter by descriptive analysis and time-intensity analysis, whereas by temporal dominance of sensations the dominant sensation was astringency, not bitterness, and that the time-intensity bitterness curves of Riesling showed no significant difference in any parameter. [rows: Sancho-Galán 2021 Palomino Fino (white): skins added during fermentation at 0% vs 100% [values in a figure only; no direction label (values not checked); no test result for bitterness in this pair]; Philipp 2024 Grüner Veltliner (white): direct pressing vs fermentation on the skins [no test, 1 pooled CATA sample; no direction label (numbers of mentions not obtained)]; Sokolowsky 2015 Riesling and Gewürztraminer (white): wines made with different skin contact times [abstract only, no values; no direction label (no values)]]
Candidate explanations for the differences
Conditions that differ between studies and could explain the differences in results, and the authors' interpretations. Several conditions differ at once, so which one mattered is unknown. These are candidates, not causes.
- In fermentation and fermentation on the skins, other components move together with the length of contact. In the fermenting Cabernet, ethanol rose from 0.6% to 14.2% with the days (Lisjak 2020). The Chenin Blanc fermented on the skins also differed from the control in pH, total acidity and fructose (Aleixandre-Tudo 2015). In Pazos 2026 the higher-alcohol wines had higher bitterness scores, and the authors guess that alcohol itself may be bitter (not checked; chaptalisation and dilution change other components too). Another study that reconstituted the same deodorised red wine (Di Fede 2026) writes that bitterness was stronger and sourness weaker with higher ethanol and higher pH, but its bitterness values are in a figure only, pH and total acidity move together and lactones were added, and it is not a row of this table. These are candidates that could explain the differences in bitterness, not causes. [rows: Lisjak 2020 Wine during fermentation: day 3 vs day 15 [ethanol also rises with fermentation]; Aleixandre-Tudo 2015 Fermentation on the skins for the whole fermentation: control vs FoS [other differences besides the skins]; Pazos 2026 Alcohol (not a contact variable): low (about 10.5%) vs high (about 16.5%) [main effect]]
- Seeds and skins differed in how bitterness moved. In Lisjak 2020 the rank sum of bitterness for the seed extract rose with the days (27 for 20 days against 11 for 3 days), while for the skin extract the text says there was no significant difference by days. The authors relate the higher astringency of the seed extract after longer extraction to a rise in the amount of high- and low-molecular-weight proanthocyanidins (a correlation in a PCA, not a cause established by this comparison alone). In Plavac mali, removing the seeds lowered bitterness (Jagatić Korenika 2023, 4.81 against 3.56 at 49 days in the 2014 vintage). [rows: Lisjak 2020 Seed extract in the model wine liquid: 3 days vs 20 days of extraction; Lisjak 2020 Skin extract in the model wine liquid: 3 days vs 20 days of extraction [text and table letters disagree]; Jagatić Korenika 2023 Seed removal: Plavac mali 2014 vintage: 49 days vs 49 days with seeds removed]
- Many conditions differ between the studies. White wines (the Chenin Blanc of Aleixandre-Tudo 2015 and the Divona of Blackford 2026) and red wines (Pazos 2026, Jagatić Korenika 2023 and others) are mixed, and the controls of the red wines already include skin contact of 7 days (Plavac mali) or 10 days (Pazos 2026), so they are not comparisons with no contact. The method of contact also differs, from extraction in a model liquid and days of fermentation to short contact before fermentation and an extension of 8 months, as do who rated (a trained panel, experts, people involved in the experiment) and the scale (rank sums, line scales, step scales). [rows: Aleixandre-Tudo 2015 Fermentation on the skins for the whole fermentation: control vs FoS [other differences besides the skins]; Blackford 2026 Divona (white): direct pressing vs 12 hours of pre-fermentation maceration at 12 °C [no mean per group, no technical replicates]; Pazos 2026 Maceration: control (10 days on the skins) vs extended (8 months) [main effect]; Jagatić Korenika 2023 Plavac mali 2014 vintage: maceration of 7 days vs 49 days]
What is not known — what this comparison alone cannot separate
- Bitterness and astringency are rated as separate items but do not always move in the same direction, and this comparison alone cannot separate which one mattered or whether they influenced each other. Fermentation on the skins in Aleixandre-Tudo 2015 raised both in the same direction, bitterness 46.70 against 30.36 and astringency 41.33 against 25.76, and the extended maceration in Pazos 2026 did too, bitterness 46.83 against 37.61 and astringency 63.72 against 35.31, but in the 2014 vintage of Plavac mali (Jagatić Korenika 2023) bitterness rose from 4.23 to 4.81 with more days while astringency fell from 3.95 to 3.71. [rows: Aleixandre-Tudo 2015 Fermentation on the skins for the whole fermentation: control vs FoS [other differences besides the skins]; Pazos 2026 Maceration: control (10 days on the skins) vs extended (8 months) [main effect]; Jagatić Korenika 2023 Plavac mali 2014 vintage: maceration of 7 days vs 49 days]
- The length of contact with skins and seeds cannot be separated from changes in alcohol, sugar, pH and acidity by this comparison alone. The extraction in a model liquid (Lisjak 2020) held ethanol constant, but it is a liquid of seeds only or skins only, not wine. Fermenting wine and fermentation on the skins (Lisjak 2020, Aleixandre-Tudo 2015) are closer to wine, but other components move at the same time. [rows: Lisjak 2020 Seed extract in the model wine liquid: 3 days vs 20 days of extraction; Lisjak 2020 Wine during fermentation: day 3 vs day 15 [ethanol also rises with fermentation]; Aleixandre-Tudo 2015 Fermentation on the skins for the whole fermentation: control vs FoS [other differences besides the skins]]
- The rows in the table are not the number of studies, and rows from the same study are not independent. The rows of Lisjak 2020 are the rankings of the same 7 people, those of Aleixandre-Tudo 2015 the same 10 people, those of Pazos 2026 the same 11 people and those of Jagatić Korenika 2023 the ratings of the same 7 experts. Studies are counted per study. [rows: Lisjak 2020 Seed extract in the model wine liquid: 3 days vs 20 days of extraction; Aleixandre-Tudo 2015 Fermentation on the skins for the whole fermentation: control vs FoS [other differences besides the skins]; Pazos 2026 Maceration: control (10 days on the skins) vs extended (8 months) [main effect]; Jagatić Korenika 2023 Plavac mali 2014 vintage: maceration of 7 days vs 49 days]
- The scale differs by study (rank sums, a 10 cm line scale, a line scale with "low" and "high" at the ends, 5 steps), so values are not compared across studies or turned into ratios. How to read the absence of a significant difference also changes with the scale and the number of people. [rows: Lisjak 2020 Seed extract in the model wine liquid: 3 days vs 20 days of extraction; Aleixandre-Tudo 2015 Fermentation on the skins for the whole fermentation: control vs FoS [other differences besides the skins]; Pazos 2026 Maceration: control (10 days on the skins) vs extended (8 months) [main effect]; Jagatić Korenika 2023 Plavac mali 2014 vintage: maceration of 7 days vs 49 days]
- The studies in which no difference was shown did not show that there is none. Blackford 2026 has no technical replicates, Magrini 2016 shows no values and its panel was people involved in the experiment, and Orbanić 2023 has the values per treatment in a figure only. [rows: Blackford 2026 Divona (white): direct pressing vs 12 hours of pre-fermentation maceration at 12 °C [no mean per group, no technical replicates]; Magrini 2016 Sangiovese (red): standard fermentation vs cold soak for 48 hours or cryomaceration [no values]; Orbanić 2023 Teran (red): standard 7 days vs 5 treatments with a 48-hour pre-treatment and extended maceration (15 or 30 days in total) [values per treatment in a figure only]]
- There is overlap in co-authors and laboratories. Orbanić 2023 and Jagatić Korenika 2023 share the co-author Jeromel, and whether the panels were the same people was not checked. Lisjak 2020 and Fontoin 2008 share the co-author Teissedre, but it was not checked whether they are the same laboratory. None is counted as an independent replication. [rows: Orbanić 2023 Teran (red): standard 7 days vs 5 treatments with a 48-hour pre-treatment and extended maceration (15 or 30 days in total) [values per treatment in a figure only]; Jagatić Korenika 2023 Plavac mali 2014 vintage: maceration of 7 days vs 49 days; Lisjak 2020 Seed extract in the model wine liquid: 3 days vs 20 days of extraction; Fontoin 2008 Alcohol (not a contact variable): varying ethanol in a model wine solution (including 11–15%) [abstract only, no values, a solution and not wine]]
- Iino 2004 reports separately the pointing-out of bitterness in skin-contact and juice fermented wines (yes or no only, no test) and a test of ethyl caprylate in ethanol solutions (a substance threshold). In the latter, 11 of 14 people pointed it out at 0.75 mg/L and 15 of 20 at 8% ethanol, but this does not prove the cause of the difference in bitterness with skin-contact fermentation, and it is read separately from the comparison of conditions. [rows: Iino 2004 Koshu (white): fermentation as juice vs skin-contact fermentation (3 days at 25 °C or 5 days at 15 °C) [yes or no only, no numbers of people, 5 people, no test; no direction label (no numbers)]; Iino 2004 Substance threshold (ethanol solution): ethyl caprylate 0 vs 0.75 mg/L (ethanol 8%) [difference in ethyl caprylate concentration; not a comparison of contact]; Iino 2004 Substance threshold (ethanol solution): ethanol 4% vs 8% (ethyl caprylate 2 mg/L) [difference in ethanol concentration; not a comparison of contact]]
How studies and rows were counted
The number of evidence rows is not the number of studies. Table rows, ledger evidence rows, papers and research groups are counted separately. Rows from the same study are scores from the same raters and are not independent. Studies that share co-authors (Orbanić and Jagatić Korenika share the co-author Jeromel, and Lisjak and Fontoin share the co-author Teissedre) were counted as separate groups, but the number does not guarantee independence. The number of research groups shown in the table below is the number of categories in the ledger, not the number of independent replications. The numbers of sources and of research groups that appear automatically below are counts of all the sources put in the table. The eight studies named at the top of the page are those mainly covered among studies in which people rated bitterness while conditions of contact were compared, and four of them published values for each condition. The difference comes from contact comparisons put on hold (because values or tests could not be checked, because the direction for pomace contact alone cannot be read, or because the direction reads the other way), studies read in the abstract only and tests in solutions that are not wine. It is counted differently, so the numbers do not match.
- Sources in the table: 14, of which 14 have results on people's bitterness ratings in this table; for the others, only results on something else (compounds, smell) are shown, or they are used only for context.
- Rows in the table (study × measured result): 30. Rows on perceived bitterness: 30.
- Evidence rows in the lab's ledger these rows rest on: 3. One paper can supply several rows. Rows without a ledger evidence row come from other tables of the same papers, or from sources newly read for this question.
- Research groups among the studies with bitterness results in this table, as grouped in the ledger: 14 (reports from the same lab count as 1; co-authors and affiliations can overlap, so this is not a count of independent replications).
What we looked at
The sources examined for this question and why each was included or excluded. We searched Europe PMC combining terms for wine, maceration, skin contact, extended maceration, cold soak, seed removal and extraction time with terms for bitterness, sensory evaluation and panels, and read papers in which bitterness appeared among the candidates with full text. We looked for open papers in OpenAlex and for Japanese studies in J-STAGE (skin-contact fermentation, skin contact, Koshu, white wine, astringency, sensory evaluation), and added the sources already in the lab's ledger. Studies using only electronic tongues or compounds, and studies with only an overall rating and no bitterness score, were not made rows in the table. For papers that stopped at a publisher's challenge page (Pazos, Jagatić Korenika, Sancho-Galán and Philipp), the challenge page was not bypassed; the text and tables of pages that opened normally in the browser were read. Of their figures, only the bitterness radar chart of Sancho-Galán was viewed (its values are rough and are not given), and supplements were not viewed. Among studies that varied ethanol, pH or acidity, there are the alcohol rows of Pazos and the abstract-only report of Fontoin, and the study of Di Fede and colleagues on reconstituted wine has its bitterness values in a figure only and no pairwise test in the text, so it is not a row and appears in a note and in a reading sentence. Within what was searched, no study that varied only pH or acidity and had people compare bitterness with readable values was found. Studies whose full text is paywalled and of which only the abstract was read were not checked for values and tests, and the rows say so. The search described here is a record, not a claim that nothing was missed.
| Source | Decision | Why |
|---|---|---|
| Effect of extraction time on content, composition and sensory perception of proanthocyanidins in wine‐like medium and during industrial fermentation of Cabernet Sauvignon (2020) doi | Included in the table | Bitterness of seed and skin extracts in a model wine liquid (3–20 days) and of fermenting wine (days 3–15) ranked by 7 people; the disagreement between text and table is in the rows; read in full |
| Effect of Skin Contact Before and During Alcoholic Fermentation on the Chemical and Sensory Profile of South African Chenin Blanc White Wines (2015) doi | Included in the table | Bitterness of the control, skin contact before fermentation and fermentation on the skins compared; a study of fermentation on the skins in white wine; an existing ledger source whose Table 5 values were rechecked; read in full |
| Impact of Harvest, Extended Maceration, and Alcohol on Sensory Profiles of Cabernet Sauvignon Wines (2026) doi | Included in the table | Main effects of extended maceration and of alcohol on bitterness compared; the alcohol rows are shown as an axis other than contact; the text and tables of the MDPI page were read (figures and supplements not viewed) |
| The Effect of Seed Removal and Extraction Time on the Phenolic Profile of Plavac Mali Wine (2023) doi | Included in the table | Bitterness by days of maceration and seed removal compared with a separate test for each vintage; seed removal is tagged as a separate finding; the methods and tables of the MDPI page were read (figures not viewed) |
| Applying Different Vinification Techniques in Teran Red Wine Production: Impact on Bioactive Compounds and Sensory Attributes (2023) doi | Included in the table | The text says bitterness was statistically equal across 6 treatments including a 48-hour pre-treatment and extended maceration (15 or 30 days in total); the values per treatment are in a figure only, which was not viewed; read in full |
| Oenological Characterization of Divona, a New Disease-Resistant Variety, and Preliminary Insights into the Influence of Maceration and Fermentation Temperature Across Three Vintages (2026) doi | Included in the table | No significant effect of pre-fermentation maceration on bitterness was shown; the row states that there is no mean per group and no technical replicates; read in full |
| On prefermentative maceration techniques: statistical analysis of sensory descriptors in Sangiovese wine (2016) doi | Included in the table | The text says bitterness was not significantly affected by the pre-fermentation treatments; no values are shown; read in full (the appendix was not viewed) |
| The Chemical and Sensory Impact of Cap Management Techniques, Maceration Length, and Ethanol Level in Syrah Wines from the Central Coast of California (2025) doi | Included in the table | The text says the only taste or mouthfeel attribute significant by Fisher's exact test was satin, but no individual result for bitterness (numbers of answers or p value) is shown. The row states that the answers are whether bitterness was less or more than a reference wine (punch down, not chaptalised); read in full (the supplement was not viewed) |
| 白ワインにおいて後味として強く残るカプリル酸エチルの苦味について (Strong Bitterness of Ethyl Caprylate as An Unpleasant Aftertaste of White Wines) (2004) doi | Included in the table | The pointing-out of a bitter aftertaste in skin-contact and juice fermentation (yes or no only, 5 people, no test) is a row on hold, and the ethyl caprylate tests in ethanol solutions are separated as substance thresholds; read in full |
| Influence of the Presence of Grape Skins during White Wine Alcoholic Fermentation (2021) doi | Included in the table | The text has the correlation between the proportion of skins and bitterness, but no result of a test of bitterness between 0% and 100%, and the values are in a figure and rough (Fig. 4 was viewed, but its values are not given); the text of the MDPI page was read |
| The Influence of Prefermentation Skin Contact, Stabulation, and Skin Fermentation on the Aromatic Behaviour and Phenolic Compounds of Important Austrian White Wine Cultivars (2024) doi | Included in the table | The wines fermented on the skins were described as bitter, but the design (1 pooled CATA sample) does not allow testing; the mentions of bitterness are only in a supplementary table (not obtained); the text of the Wiley page was read |
| Effects of Prolonged Pomace Contact on Color and Mouthfeel Characteristics in Merlot Wine During the Ageing Process Under Microwave Irradiation (2025) doi | Included in the table | A design crossing the presence of pomace with microwave treatment; in the sensory paragraph the subject that lowered bitterness is the microwave treatment, and the direction for pomace contact alone cannot be read from the text. There is no test of the sensory results, and the values are in a figure (not obtained). Kept as a row on hold; read in full |
| Sensory impact of skin contact on white wines characterized by descriptive analysis, time-intensity analysis and temporal dominance of sensations analysis (2015) doi | Included in the table | The white wine fermented completely on the skins was significantly more bitter by descriptive analysis and time-intensity analysis; only the abstract was read, and values, numbers of people and pairwise tests are unconfirmed; an existing ledger source |
| Effect of pH, ethanol and acidity on astringency and bitterness of grape seed tannin oligomers in model wine solution (2008) doi | Included in the table | A study varying ethanol in a model wine solution; only the abstract was read, and values and direction cannot be checked; shown as a reference for the ethanol, pH and acidity axis; an existing ledger source |
| The Impact of Fermentation Temperature and Cap Management on Selected Volatile Compounds and Temporal Sensory Characteristics of Grenache Wines from the Central Coast of California (2023) doi | Read as context (not in the table) | A comparison of punch down against none and of fermentation temperature, not of the length of contact. It gives time curves of the citation proportion in TCATA, not a score of bitterness intensity (8 trained panellists; only the cold-fermented wine without punch down had a significantly lower citation proportion of bitterness, from 11 to 46 s). The same Casassa laboratory as Stoffel 2025; read in full |
| Impact of climate‐induced compositional shifts of ethanol and acidity on aroma release and perception in red wine: a case study on γ‐nonalactone and massoia lactone (2026) doi | Read as context (not in the table) | The same deodorised red wine was reconstituted into 3 × 3 combinations of ethanol at 12, 14 and 16% and pH/total acidity (3.2/8, 3.6/6.5 and 4.0/5 g/L), and taste alone was rated by RATA with nose clips (16 trained people). The text writes that bitterness was stronger and sourness weaker with higher ethanol and higher pH, but the bitterness values are in a PCA figure only and the text has no pairwise test. pH and total acidity move together and lactones were added. It is not a comparison of contact with skins and seeds, so it is not a row; it appears in the note of the alcohol rows and in a reading sentence. Read in full (CC BY) |
| Exploring the Impact of Extended Maceration on the Volatile Compounds and Sensory Profile of Monastrell Red Wine (2024) doi | Excluded | The methods mention rating bitterness, but the axes of the radar chart in Fig. 2 have no bitterness and the text gives no result for bitterness (18 consumers; astringency was lower with the extension). With no result for bitterness it is not a row; the MDPI page was read |
| Commercial Mannoproteins Improve the Mouthfeel and Colour of Wines Obtained by Excessive Tannin Extraction (2021) doi | Excluded | The bitterness comparison is only with or without mannoprotein within each wine type, and there is no test of bitterness between the extended-maceration and free-run types; read in full |
| Enhancing the color and astringency of red wines through white grape seeds addition: Repurposing wine production byproducts (2024) doi | Excluded | A study adding seeds of a white grape (Gewürztraminer) to Cabernet Sauvignon must before fermentation, which is not a comparison changing the length or method of contact with the skins and seeds of the same grapes, so it is not a row. On bitterness, 17 people rated the wines after 4 months in bottle, bitterness was rated as one aspect of tannin texture, and the text says adding seeds did not affect the intensity of bitterness (and says this agrees with the electronic tongue). Whether there is a separate bitterness scale, values or a test was not checked, because Fig. 4C and supplementary table S5 were not obtained; read in full |
| Maceration in White Winemaking: Enhancing Phenolics, Volatile Aromas and Sensory Characteristics of Chardonnay and Italian Riesling Wines (2026) doi | Excluded | The sensory evaluation has no bitterness attribute (the work is mainly chemical analysis), so there is no result for bitterness; checked in the Europe PMC full text |
| Effects of Different Maceration Times on the Chemical and Sensory Characteristics of Cabernet Sauvignon Grapes Wine (2026) doi | Excluded | The sensory evaluation has no bitterness attribute, so there is no result for bitterness; checked in the Europe PMC full text |
| Phenolic Evolution During Extended Skin Contact: Effects of Harvest Maturity on “Orange” Wine Composition and Color (2026) doi | Excluded | A study of composition and colour with no sensory result for bitterness; checked in the Europe PMC full text |
| The effects of the duration of cold maceration on the composition and sensory properties of Smederevka wines (2016) | Excluded | A 100-point overall rating of wines with cold maceration of 12 and 24 hours, with no bitterness attribute (Advanced technologies 5(2):60-63); checked in the full PDF |
| 白ワイン醸造に関する研究 仕込みにおける除梗およびマセレーションの影響 (1973) doi | Excluded | A comparison of destemming and maceration in Koshu, but the sensory evaluation is an overall tasting of the new wine and does not rate bitterness; checked in the J-STAGE PDF |
| Bitter Taste of Higher Alcohols in Wine (1994) doi | Excluded | Tests of the presence of bitterness in wines from 10 yeast strains and of adding isoamyl alcohol and others to a model wine (pointed out by 3 people): a test of substances, not a comparison of conditions of contact; from the same Yamanashi prefectural centre as Iino 2004; checked in the J-STAGE PDF |
| Astringency and bitterness of selected phenolics in wine (1990) doi | Excluded | By its title and abstract it is a study adding phenolics, not comparing conditions of contact with skins and seeds, so it is not a row (the full text was not read) |
| Towards an understanding of bitterness in white wines: Contribution of 27 compounds assessed by LC-HRMS and sensory analysis (2024) doi | Excluded | A study of the correlation between compounds and bitterness in commercial white wines that does not compare conditions of contact; only the abstract was read |
| Influence of grape maturity and maceration time on sensory characteristics and phenolics in Pinot noir and Cabernet-Sauvignon wines (2025) doi | Full text not reachable | It appears to vary maceration time, but the publisher's site could not be reached and it was not obtained; values and tests were not checked |
| Balancing phenolic maturity and alcohol content: The impact of seed removal on red wines (2025) doi | Full text not reachable | It appears to concern seed removal, but the publisher's site could not be reached and it was not obtained; values and tests were not checked |
| Evolution and impact of extended pomace maceration in red wines: Chromatic, phenolic and sensory perception (2025) doi | Full text not reachable | A study of extended maceration, but the publisher's page was not obtained (copies in university repositories and drafts are not used); values and tests were not checked |
| Influence of skin maceration and Torulaspora delbrueckii inoculation on white wine production: changes in fermentation dynamics and wine composition (2025) doi | Full text not reachable | A study of skin maceration of white wine, but the publisher's page was not obtained; values and tests were not checked |
| Chemical studies on coloring and flavoring substances in Japanese grapes and wines. Part XXVI Production of wines from unripe Koshu and Cabernet Sauvignon grapes, and wild grapes by carbonic maceration. (1986) doi | Full text not reachable | A study of carbonic maceration. The J-STAGE page shows no free-access mark and the full text was not obtained; values and tests were not checked |
Read in the encyclopedia
- Skin contact (skin maceration) — the entry for leaving skins and seeds in contact with the must
- Wine — the entry on the bitterness and astringency of wine
- Bitterness, Astringency, and Egumi — the page on how the three tastes differ and how they are recorded
Source ledger
Each study's source can be reached from its section above. All of the lab's sources are listed in the source ledger.
How to cite this page
Aoki, M. (NIGAMI LAB) (2026). Does skin and seed contact change how bitter wine is?. https://nigamilab.com/en/topics/wine-skin-contact-bitterness/
Each claim card has a stable anchor (#clm-…). The dataset is CC BY 4.0; see the data page. Dataset DOI: 10.5281/zenodo.22739101