bitterness

Scope: Layer: food. Fresh spinach leaves, water extract, and boiling liquid, and their solid-phase extraction fractions (water-eluted fraction / ethanol-eluted fraction). Sensory evaluation by a small number of people (including the authors).

Note: The source states 「ホウレンソウの苦味については、シュウ酸とは異なる成分によるものと考えられる」 (in translation: "the bitterness of spinach is considered to be due to a component distinct from oxalic acid") — its own conclusion that the oxalate taste (the subject of the egumi debate) and bitterness are not the same substance. As a separate proposition supporting the existing claim that oxalate taste can be measured apart from bitterness, this is the identification-side conclusion that spinach's bitter substance is not oxalic acid.

Scope: Layer: solution. Taste comparison of protein-hydrolysate-derived Maillard reaction products (MRPs) with cysteine added.

Note: The review summarizes a primary study, but its relevant passage gives no specific reduction percentage, statistics, or comparator conditions.

Scope: Layer: food. Coarse white sesame seeds from China, 1994 crop (Kadoya Sesame Mills), roasted in an electric oven at 170, 200, or 230°C for 1 to 20 minutes (12 conditions). Taste-related components — free sugars (mainly sucrose) and free amino acids (mainly glutamic acid, aspartic acid, alanine, and others) — were quantified by HPLC and a high-speed amino-acid analyzer.

Note: The total free amino acids and the amount of free sugars decreased consistently as roasting temperature and time increased (for example, total free amino acids fell to 23% of the unroasted level at 170°C for 20 minutes, and to 44% at 230°C for 10 minutes; free sugars, mainly sucrose, had almost disappeared at 230°C for 10 minutes, with a residual rate of 0.2%). The authors discuss these taste-related components as 『甘味を中心に、酸味あるいは苦味とともに呈味に寄与している』 (in translation: "contributing to taste mainly through sweetness, together with sourness or bitterness"), but bitterness was not measured as an independent sensory score (the 5-point sensory evaluation covered color, shape, aroma, taste, and overall impression). No source directly measuring the bitterness of roasted sesame itself was found within the range of this collection.

Scope: Layer: literature. A quality-evaluation vocabulary system for sake's aroma and flavor (86 terms, 16 classes). An additional angle drawing on Utsunomiya et al. 2006, the existing source on sake flavor vocabulary (already read in full).

Scope: Layer: literature. Chromatographic isolation from the above-ground parts of Centaurium erythraea and structural determination by UV, IR, and NMR (published in 1976).

Scope: Layer: literature. Discussion in a bitterness study of juice from Citrus and Citrus × Poncirus trifoliata hybrids.

Scope: How it is felt when eating or drinking food or beverages

Note: The two can occur together and each can affect how the other is felt, but bitterness as a taste and astringency as a dryness/roughness are recorded separately. / 2026-08-31: Calibration downgrade from established to supported, because the supporting evidence does not derive from a full-text check. Can be re-upgraded after a full-text check.

Scope: Some food tannins and polyphenols

Note: Not all tannins have the same receptor and sensory profile.

Scope: Highly hopped commercial beer

Note: The contribution was modeled together with isohumulones and ethanol; it is not a universal explanation by a single compound.

Scope: Brewed green tea

Note: Intensity depends on the tea leaf and brewing method. / 2026-08-31: Calibrated down from established to supported, because the supporting evidence does not derive from a full-text check. May be re-upgraded after a full-text check.

Scope: A 2005 report identified 25 diketopiperazines, of which DoT > 1 in 5; a subsequent report shows contribution of 7 compounds.

Scope: In many of the citrus products where it occurs, an immediate bitterness contribution

Note: How much is present and how much it matters differ by citrus species and product.

Scope: In many of the citrus products where it occurs, a delayed bitterness contribution

Note: Matrix and precursor conversion affect how it is perceived over time.

Scope: Specific glucosinolates within Brassicaceae

Note: Some individual glucosinolates impart bitterness, but total content is an insufficient proxy for sensory outcome. / 2026-08-31: Calibrated down from established to supported because the supporting evidence has not been confirmed via full text. Can be re-upgraded once the full text is confirmed.

Scope: Naturally processed green olives investigated during processing

Note: Other phenolic compounds and processing conditions also contribute to final sensory quality.

Scope: 100 extra virgin olive oil samples from 6 cultivars and 7 countries

Note: The reported correlation r = 0.72 is neither causal nor a universal calibration.

Scope: Commercial beers in the cited hop-profile study

Note: The type of hop acid, its oxidation state, and the beer matrix affect its temporal character.

Scope: Commercial lager rich in polyphenols in the cited research

Note: Polyphenols are a heterogeneous class and may contribute to mouthfeel as well. They do not carry a fixed intensity across the class.

Scope: Green tea infusion in the cited quantitative study.

Note: The correlation is specific to concentration and matrix.

Scope: Green tea infusion in the cited quantitative study.

Note: Correlation is specific to concentration and matrix.

Scope: Aqueous reconstitution and removal trials of roasted cacao nibs.

Scope: Chicory and chicory-based coffee substitute in the cited research

Note: Receptor activation together with the concentration in the food forms perception.

Scope: Chicory and chicory-based coffee substitute in the cited research

Note: Receptor activation together with the concentration in the food forms perception.

Scope: Quinine hydrochloride solution in human taste tests

Note: Intensity varies with concentration and mixture context.

Scope: Electronic taste-sensor response to fractionated coffee extract

Note: The cited experiment does not provide confirmation by human sensory evaluation.

Scope: Roasted cacao nibs and taste reconstruction in a water-based system

Note: The finished chocolate requires a separate matrix and process record. / 2026-08-31: Calibrated down from established to supported because the supporting evidence does not derive from a full-text check. May be re-upgraded once the full text is checked.

Scope: Orange juice investigated by sensory-guided metabolomics.

Note: Cultivar and processing must be retained for each sample. / 2026-08-31: downgraded from established to supported because full-text verification is absent in supporting evidence. Upgrade is possible after full-text review.

Scope: Purified compound in 3% ethanol, in the threshold study cited

Note: Threshold and contribution are matrix-specific.

Scope: Purified compound in 3% ethanol, in the threshold study cited

Note: Threshold and contribution are matrix-specific.

Scope: International standard terminology concerning sensory attributes.

Note: The text of the definitions has not been reproduced. Full-text access is paid.

Scope: Cacao liquor. 2 independent trained panel studies with instrumental quantification.

Note: The discrepancy is among studies using different materials and different statistics. Neither report contains coefficients in the text we read.

Scope: Beta-acid transformation products from heat treatment of colupulone under wort-boiling conditions. Subsequently quantified in commercial beer

Note: Shows that not only alpha-acid derivatives but also hop beta-acids contribute measurable bitterness, and that even at similar threshold magnitudes, the temporal quality differs among homologs. Panel size and threshold method are not stated in the abstract.

Scope: The principal hop-derived bitter substance in beer. Its human detection threshold has been measured in a hop-free lager base

Note: An isomerization-product class within the hop bitter acid family (compound-hop-bitter-acids). / 2026-08-31: calibration-downgraded from established to supported because the supporting evidence has no full-text-checked source. May be re-upgraded once full text is checked.

Scope: Cooked Brassica vegetables (Brussels sprouts, cauliflower, turnip) evaluated by trained analytical panels

Note: Studies that sum specific glucosinolates (sinigrin, progoitrin, neoglucobrassicin) report a strong correlation, while a study correlating total glucosinolate content across batches of steamed turnip found the relationship not significant. The sampling unit (cultivar or batch), which glucosinolates are summed, and n differ across studies.

Scope: UK adult consumers who rated rocket (arugula) lines (genotyped n=69) and cooked turnip (n=74). TAS2R38 PAV/PAV, PAV/AVI, and AVI/AVI diplotypes

Note: The main effect of genotype on bitterness was significant in both studies, but in neither study did pairwise comparisons within individual samples separate the genotypes.

Scope: A systematic review and meta-analysis of 72 studies (36 of which were meta-analyzed) in adults without chronic disease. Bitterness sensitivity was measured by phenotype (PROP/PTC) or genotype (TAS2R38)

Note: An upper-bound finding across the literature that individual differences in bitterness sensitivity explain little of adult eating behavior. The authors point out that the influence of study design and dietary assessment method may be larger than the phenotype/genotype distinction.

Scope: US psychophysical studies and genotype-phenotype studies synthesized in the cited review

Note: That sensitivity changes with age even within the same genotype is the developmental background for 『獲得嗜好』 (in translation: "acquired taste"). The timing of the shift to the adult pattern (adolescence) is the review's summary phrasing, and the numbers from individual studies have not been confirmed.

Scope: Fresh leaves; the origin of the common name 「ビターリーフ」 (in translation: "bitter leaf").

Scope: Used as a bitter-beverage category item in a multiple-sip time-intensity study with an Argentine consumer panel

Note: The same study confirmed a cumulative effect in which maximum bitterness intensity increased with each successive sip. The intensity value for mate alone is not given in the abstract.

Scope: EFSA description of wild Lupinus seeds (bitter tasting QAs).

Scope: Wild almond and bitter-kernel lineages.

Note: Not psychophysical bitterness measurements, but standard descriptions in plant science literature.

Scope: The crude-drug description in the Japanese Pharmacopoeia

Note: The original text states 「味は苦くて，僅かに刺激性」 (in translation: "the taste is bitter, with slight pungency"). This is not an intensity measurement by a food sensory panel.

Scope: The taste of the midrib under the EU specification

Note: Describes "pleasant somewhat bitter" and "crunchy" as separate attributes.

Scope: The late type under the EU specification

Note: Recorded as "slightly bitter".

Scope: EU specification’s tipo tardivo

Note: Slight bitterness is listed as a typical attribute after forcing and blanching.

Scope: Artichoke's characteristic bitterness

Note: A review's synthesis of primary research.

Scope: A sensory-threshold study of sesquiterpene lactones from chicory.

Note: This is the threshold of an isolated compound, without accounting for its concentration in food.

Scope: A sensory-threshold study of sesquiterpene lactones from chicory.

Note: Its contribution within a food matrix has not been established.

Scope: An evaluation after repeatedly taking EGCG, a type of tea catechin, dissolved in water for 2 weeks

Note: This is a comparison with repeating water alone, and does not show a mechanism of becoming accustomed to all foods.

Scope: A task in which sweet, sour, salty, and bitter samples were identified separately from astringent and pungent samples, presented on different test strips

Note: This is a result showing that separate answer columns could be used to measure them; it is not proof that each sensation is received by only one kind of sensor.

Scope: The final product of naturally fermented olives across 5 cultivars

Note: The amount of bitterness-related phenolics differed among cultivars, but there was no significant difference in the final perceived bitterness rated by an 8-member panel. This does not mean chemical quantity in general is irrelevant.

Scope: Temporal Dominance of Sensations (TDS) with 30% milk or oat drink added to medium- and dark-roast coffee

Note: The dominance rate of bitterness dropped in several time windows, including the early period. This does not assert intensity reduction, removal of taste substances, or a mechanism attributable solely to fat or protein.

Scope: A single study that passed water-extracted components of spinach through an adsorbent and separated them into two groups with different properties

Note: "Oxalate taste," a term given its meaning within this study, collected on the side that washed out with water, while bitterness collected on the side subsequently extracted with ethanol. This is not a claim that egumi in every food derives from oxalate.

Scope: Volatile compound analysis of Doi Chang-grown arabica (HS-SPME-GC/MS, comparing light, medium, and dark roasts)

Note: The body of the paper connects the change in furfuryl alcohol content with roast level to a description, via the Maillard reaction, that 「焦げた・ロースト香が苦味として知覚される(perceived as a bitter taste)」. However, this description is a discussion grounded in other literature, not the study's own human sensory measurement, so it is treated as contextual.

Scope: The sensory description of the precoce type in the original Italian-language disciplinare (Art. 6, comma 2, lettera c)

Scope: "Las saponinas del género Chenopodium se caracterizan por poseer un sabor amargo y propiedades surfactantes"(in translation: "Saponins of the Chenopodium genus are characterized by having a bitter taste and surfactant properties") — a genus-level generalization in the paper.

Note: Not a direct record of sensory testing, but background description summarizing prior literature.

Scope: Colonial-era record: el cacao con agua y sin dulce es muy amargo (in translation: "cacao with water and without sweetness is very bitter") (Robelo 1904). Molina's Vocabulario (1555/1571) explains the reason the word cacao solo (an unsweetened cacao drink) does not appear in other sources as no se bebía mucho, era muy amargo (in translation: "it was not drunk much — it was very bitter").

Note: A historical, discursive record based on Spanish-language documents from the 16th to the 20th century, not a modern sensory measurement.

Note: An explicit connection between zatsumi and bitterness, based on Utsunomiya et al.'s (2006) operational definition (bitterness, umami, astringency, and other unpleasant mouthfeel tastes).

Scope: Group A saponin fraction isolated from unprocessed soybean (sensory evaluation)

Note: Okubo (1988) isolated the major components of soybean group A saponins (Aa, Ab, etc.) and their aglycones (soyasapogenol A, B, E) and investigated their taste thresholds and taste qualities by sensory evaluation, showing that group A saponins have the lowest taste threshold and exhibit strong bitterness and astringency. Tsukamoto (2012) also reviews that 「ソヤサポゲノールAをアグリコンとするグループAサポニンは不快味の原因成分であると報告されている」 (in translation: "group A saponins with soyasapogenol A as the aglycone are reported to be causative components of the undesirable taste").

Scope: Isoflavone glycosides (daidzin, genistin, etc.) isolated from raw, unprocessed soybean (sensory test)

Note: Okubo (1988) conducted a sensory test on genistin and daidzin, the main isoflavonoids of soybean, and their aglycones (genistein and daidzein), and showed that the isoflavonoid components exhibit a strong astringent taste and bitterness at a taste threshold of 10⁻²–10⁻³ mM.

Scope: 6 brands each of commercial raw soy sauce and heat-treated (hiire) soy sauce (6 matched pairs from the same manufacturers), compared by QDA (quantitative descriptive analysis) with a trained panel of 13, women aged 32–62

Note: In Imamura & Katayama's (2017) QDA, heat-treated soy sauce showed significantly higher, or a differing tendency in, evaluation scores for bitterness, astringency/egumi, and bitter aftertaste compared with raw soy sauce (Wilcoxon signed-rank test). In the principal component analysis as well, bitterness, astringency/egumi, and bitter aftertaste showed strong positive loadings on PC1 (0.95, 0.94, and 0.93 respectively; 69.3% contribution rate), and heat-treated soy sauce was plotted in the positive direction of PC1. Note that this is the heat-sterilization process itself, not a change in the fermentation process.

Scope: Trained-panel sensory evaluation of 25 commercially available U.S. shredded Cheddar brands (2 lots each), followed by consumer preference ratings of 10 representative brands by 151 consumers; analyzed with analysis of variance, principal component analysis, and external preference mapping.

Note: Bitterness was identified as one driver of overall dislike. A powdery appearance also lowered appearance and overall liking ratings.

Scope: A study relating sensory profiles before and after heating to physicochemical parameters in 4 categories of AOP/PDO blue cheeses from France's Massif Central: Fourme d'Ambert, Fourme de Montbrison, Bleu d'Auvergne, and Bleu des Causses. Along with saltiness and sourness, bitterness was recorded as one of the basic tastes distinguishing these 4 categories after heating, and correlations with physicochemical parameters were also shown.

Note: The paper does not describe bitterness as either a 『欠陥』 (in translation: "defect") or a 『望ましい風味』 (in translation: "desirable flavor"). It treats it neutrally as an attribute distinguishing categories; this entry likewise does not overstate its significance. No peer-reviewed paper addressing bitterness in Gorgonzola itself was found, so the study of French AOP cheeses is included as a related blue-cheese lineage (see the corresponding research lead).

Scope: Fully ripe fruit of wild cherry tomato (Solanum lycopersicum var. cerasiforme) from Peru's Río Mayo valley.

Note: Cárdenas et al. 2019 presents this association in its text as a citation of earlier work by Charles Rick and colleagues. It was not a new, independent human sensory test conducted by Cárdenas et al. themselves.

Scope: Earlier sensory analysis cited by Pegiou et al. 2021.

Note: Saponin concentration is reported to be higher in the white type, yet the bitter note is assigned to the green type. This is recorded as an example where metabolite amount and flavor attribution do not correspond simply.

Scope: Wine made from grapes exposed to wildfire smoke (Merlot, smoke-treatment plots of eucalyptus, pine, and wild oat, exposed 14 days after flowering)

Note: Glycoconjugates (glycosidically bound forms) of phenol, m-cresol, and p-cresol correlated strongly with the sensory attributes of bitterness, ashiness, sourness, metallic taste, and astringency (dryness). It is reported that free (volatile) phenols correlate with negative aroma attributes while the glycoconjugates correlate with negative taste attributes — a chemical correlation pattern that differs between aroma and taste. Prior research (Toth & Potthast, original text unconfirmed) describes phenol, cresols, guaiacol, and 4-methylguaiacol as 「熱く、苦い味」 (in translation: "hot, bitter taste"), which the authors state is consistent with this study's correlation pattern.

Scope: A comparison before and after the pine-smoke withering process for lapsang souchong (smoked tea)

Note: Using a method integrating electronic-tongue analysis, sensory evaluation, and a cell-based calcium-imaging assay, the pine-smoke withering process was confirmed to significantly reduce the tea's bitterness. The study reports that non-targeted metabolomics found pine-smoke withering to have greatly decreased the major bitter phenolics, including 10 monomeric catechins, 14 glycosylated flavonols, and 6 galloylated phenolic acids. The full text has not been confirmed; this is abstract-level information.

Scope: Unsweetened cranberry juice (CJ), descriptive sensory evaluation using a 15-cm line scale.

Note: Unsweetened cranberry juice was reported to show strong sourness, sparse sweetness, and 『moderately-high bitterness, astringency, cranberry flavor(中程度から高い苦味・渋味・クランベリー風味)』 (in translation: "moderately-high bitterness, astringency, cranberry flavor").

Scope: Polyphenol-rich aronia berry juice; descriptive sensory panel of 50 participants rating sweetness, sourness, saltiness, bitterness, astringency, and liking.

Note: As the harvest progressed, the study reports that astringency declined to 『just above weak(弱いよりやや上)』 (in translation: "slightly above weak") and bitterness to 『just below weak(弱いよりやや下)』 (in translation: "slightly below weak"). Bitterness was described as showing no significant correlation with any of the measured chemical constituents.

Scope: A comparison of texture design using unsweetened freshly pressed lingonberry juice.

Note: Unsweetened freshly pressed juice is described as 『naturally bitter, sour and astringent(自然に苦味・酸味・渋味を持つ)』 (in translation: "naturally bitter, sour and astringent").

Scope: A narrative review of consumer research (bitterness acceptance in EVOO and Brassicaceae)

Note: The review states that “although bitter taste is a general driver of dislike,” and for Brassica vegetables specifically, that “consumers generally prefer such vegetables cooked as they are less bitter and pungent.” As an industry response, it cites “the elimination of bitter substances from vegetables ... and the use of sweet masking substances.” This is a minimal addition to the 『産業は苦味を抜く』 (in translation: "industry removes bitterness") side, connecting to existing assets on Brassica breeding and acquired liking.

Scope: The roots of 3 chicory (Cichorium intybus) cultivars grown in northern France

Note: A follow-up investigation into an item that had been deferred (11beta,13-dihydrolactucin). The existing claim had only compositional information -- content that rose or fell in the root -- with no connection to bitterness. This one is based on primary material that directly links the compound to bitterness: a correlation between the ELISA-quantified value and the sensory panel's bitterness assessment (r>0.9). Because the body text has not been read in full, this is kept as supported rather than established.

Scope: Koicha is matcha made by finely grinding tencha and kneading it at high concentration. The source deals with sensory evaluation methods for matcha generally, not koicha specifically, and does not describe bitterness separately for koicha and usucha.

Note: The taste vocabulary table for matcha sensory evaluation at the Tea Industry Research Institute lists 「苦味」 (in translation: "bitterness") as an independent item and says excessive grinding or deterioration may increase it. If the amount processed by the mill per unit time falls below the standard condition (resulting in excessive grinding), a heated or scorched taste accompanied by bitterness may occur. The report considers the longer heating caused by tea leaves remaining in the mill to be the cause. The table lists 「青臭味や覆い香味不足」 (in translation: "grassy odor or insufficient covered-tea aroma"), 「苦味」 (in translation: "bitterness"), 「ざらつき」 (in translation: "grittiness"), and 「芳香味不足」 (in translation: "insufficient aromatic flavor") as parallel categories. It treats bitterness as a separate defect term from astringency or acridity. The taste-evaluation vocabulary does not itself use the word astringency.

Scope: Cucurbitacin C in the fruit and leaf tissues of cucumber (Cucumis sativus)

Scope: Based on the entries GENZIANA and TINTURA DI GENZIANA in the first edition (1892) of the Farmacopea Ufficiale del Regno d'Italia.

Scope: Based on the TINTURA DI CHINA entry in the first edition (1892) of Farmacopea Ufficiale del Regno d'Italia.

Scope: Based on the expression 『dolce-amaro』 (in translation: "sweet-bitter") on Averna's official site.

Note: A corporate promotional expression, not a sensory evaluation.

Scope: 「石橋徳雄」 (in translation: "Ishibashi Tokuo") 「ビールの官能評価について」 (in translation: "On the Sensory Evaluation of Beer"), Journal of the Brewing Society of Japan, volume 84, issue 6 (1989), page 361; a commissioned review article in the journal (1989).

Note: A review article in the field of beer sensory evaluation that positions bitterness as one of the 4 basic tastes constituting taste in its narrow sense.

Scope: Ishibashi Tokuo, "On the Sensory Evaluation of Beer," Journal of the Brewing Society of Japan, vol. 84, no. 6 (1989), p. 362. A commissioned commentary article in the Journal of the Brewing Society of Japan (1989).

Note: A statement citing a report by Owaka and Kokubo (the original paper is only indicated by citation number 24 within this article, and that original paper itself has not been checked directly).

Scope: Majid et al. (2018), PNAS 115(45), Methods and the Figure 2 caption. Data from 313 speakers of 20 languages (including 3 sign languages).

Note: A primary source for the fact that the ease of naming tastes can differ by market and language.

Scope: Majid et al. (2018) PNAS 115(45), Results『Relative Codability of the Senses』

Scope: O'Mahony & Ishii (1986), British Journal of Psychology 77(2), Abstract

Note: Only the abstract was checked; the full text (details of the stimuli and number of participants) was not.

Scope: O'Mahony & Manzano Alba (1980), Chemical Senses 5(1):47-62, Abstract

Note: Only the abstract was checked; the full text was not.

Scope: Robinson (1970) British Journal of Psychology 61(3):375-378, Abstract

Note: Only the abstract was checked. Details such as stimulus concentrations and participant count were not checked.

Scope: Winter (2016) Language, Cognition and Neuroscience 31(8):975-988, Abstract

Note: Only the abstract was checked. The analysis is based on English corpora, including COCA; the abstract has no numerical results specific to bitterness words.

Scope: Codex medicamentarius Gallicus, 1908 edition (Internet Archive item codexmedicamenta0000phar), the relevant body-text entry

Note: A direct statement in which the official French pharmacopoeia explicitly gives "amère" (bitter) as a property of the gentian tincture.

Scope: Codex medicamentarius Gallicus, 1908 edition (Internet Archive item codexmedicamenta0000phar), the relevant body-text entry

Note: A sequential taste description for the yellow cinchona extract: "sweet at first, then a weak bitterness." The same pharmacopoeia's "EXTRAIT DE QUASSIA" entry uses the stronger expression "saveur très amère" (in translation: "a very bitter taste").

Scope: Full text of the ANSM public PDF (gentiana-lutea-pph.pdf); in force as of 2026-09-04

Note: Even in the current official French pharmacopoeia, the word "amère" (bitter) is stated explicitly in the description of gentian root's properties.

Scope: The entries GENZIANA and TINTURA DI GENZIANA in the 2nd (1902) and 3rd (1909) editions of the Farmacopea Ufficiale del Regno d'Italia

Note: The same wording as the first edition (1892) of the same entry (the existing claim (w58h4b) on gentian-root bitterness in the 1892 Farmacopea) — "sapore prima dolciastro, poi amarissimo persistente" and "sapore molto amaro" — is confirmed again in the 1902 and 1909 editions, bearing out the continuity. Because the GENZIANA (root) entry in the 1902 edition was hard to read owing to OCR column misalignment, the verbatim confirmation for this claim rests on the TINTURA DI GENZIANA entry ("sapore molto amaro" in both the 1902 and 1909 editions) and the GENZIANA entry ("sapore prima dolciastro, poi amarissimo persistente" in the 1909 edition).

Scope: The CHINA (yellow and red cinchona bark) entry in the 2nd (1902) and 3rd (1909) editions of the Farmacopea Ufficiale

Note: The same statement as the first edition's (1892) CHINA entry, "sapore amaro", is confirmed again in the 1902 and 1909 editions. In the 1909 edition, both the yellow and red cinchona varieties each carry their own "Sapore amaro" entry.

Scope: The TINTURA DI CHINA entry in the 3rd edition (1909) of Farmacopea Ufficiale.

Note: The same wording as the entry in the first edition of 1892 (『sapore astringente ed amaro』 (in translation: "astringent and bitter taste")). No corresponding entry was found in the portions read of the 1902 edition; whether it was absent from that edition or overlooked remains unknown.

Scope: The product page of the official website (santuariodimontevergine.it)

Note: The product name itself is "l'amaro Benedettino", and the maker itself presents the product using the word "amaro". There is no direct sensory description (a taste evaluation stating "bitter" as such) in the body of the page; the judgment rests on the use of "amaro" as a product-category name.

Scope: Layer: food. Italian PDO "Oliva di Gaeta." Quantitative descriptive analysis on an unstructured 0-10 scale by a 10-member panel of students and researchers from the University of Naples Federico II.

Scope: Layer: food. Spanish-style Manzanilla green olives. Evaluation by a consumer panel of 100 with 3-10 years' experience regularly eating green olives. A 14-formulation experimental design.

Scope: Layer: food. The same test, the same study, the same panel.

Note: An example showing that not every substitute for sodium salt weakens bitterness.

Scope: Layer: food. Human sensory evaluation using actual vegetables (Brussels sprouts, cauliflower).

Scope: Layer: solution (cocoa-flavor model system). Split-tongue method, 65 participants (18-35 years old), 2 sessions -- a normal condition and a sweetness-blocked condition.

Note: A result from a model system, not from actual chocolate as a food.

Scope: Layer: solution. Binary sweetener mixtures formulated to a target sucrose-equivalent sweetness, with human sensory evaluation.

Note: The bitterness at issue is that of acesulfame K and saccharin themselves, not other bitter components in food.

Scope: Layer: solution. An untrained taste-term labeling test with British and American participants using sucrose, citric acid, sodium chloride, and quinine sulfate solutions (Chemical Senses 4(4):301-318).

Scope: Layer: solution. One side of the front half of the human tongue dorsum was pretreated with capsaicin (high concentration 33 ppm/109 uM, low concentration 1.5 ppm/4.9 uM) and compared with the untreated side. 5 stimuli (sucrose, NaCl, quinine, monosodium glutamate, citric acid) were applied to both sides and compared using 2-alternative forced choice and intensity ratings.

Note: A significant proportion of subjects rated the quinine bitterness, sucrose sweetness, and glutamate umami on the non-treated side as stronger. There was no difference between the two sides for saltiness or sourness. After a 15-minute break (allowing the capsaicin burn to disappear and desensitization to occur), the difference between the two sides disappeared.

Scope: Layer: solution. Experiment 1 involved 12 healthy adults. Experiment 2 involved 30 healthy adults, including 15 who participated again to assess reproducibility. Piperine-impregnated taste strips (6 concentrations, 1–25 mg/dL) were applied to the tongue tip for 15 seconds to assess intensity and duration; they were paired with bitter, sweet, or blank strips for a spatial-localization task.

Note: A pilot study in healthy adults: experiment 1 (n=12) and experiment 2 (n=30, including 15 retested to assess reliability).

Scope: Layer: solution. Threshold table cited by the review as Table 2 (the original source is a work the review cites).

Note: Transcribed from the review's table. Measurement conditions in the original source are unverified.

Scope: Layer: Literature (secondary citation). In the Introduction of Gigl et al. 2026 (JAFC, full text read), a numerical value stated by citing Chen, W.C. (1979, doctoral dissertation, University of Munich, German, not read in the original—secondary citation).

Note: The source (Chen 1979) is accessed via secondary citation; the original has not been read. Care should be taken regarding the provenance of the numerical value.

Scope: Layer: literature (secondhand citation). A figure stated in the Introduction of Gigl et al. 2026 (JAFC, full text read), citing Chen W.C. (1979, a doctoral dissertation at the University of Munich, primary source not read — a secondhand citation).

Scope: Layer: food. A 3-AFC method in which panelists identified 1 added-caffeine cup among 3 cups, 2 of which were decaffeinated coffee (control).

Scope: Layer: food. High-molecular-weight fraction isolated from coffee by ultrafiltration (fractionation molecular weight 10 kDa) was reconstituted in bottled water and evaluated on a 0-5 scale by 18 panelists.

Scope: Layer: Solution (direct application to tongue surface). Detection thresholds were measured when 9 cardiovascular medications (propranolol HCl, labetalol HCl, captopril, diltiazem HCl, enalapril maleate, hydrochlorothiazide, mexiletine HCl, procainamide HCl, and propafenone HCl) were applied to human subjects in younger and older age groups.

Scope: Layer: food. Sensory analysis in which a trained panel classified 200 EVOO samples, produced across 2 crop seasons, into 3 regulatory categories (Delicate, Medium, Robust), together with phenolic-content analysis estimating each compound's contribution via ROC analysis.

Scope: Layer: food. Electronic-tongue analysis and sensory evaluation comparing processing stages for 2 oolong cultivars, Tieguanyin and Jinguanyin.

Scope: Layer: Food. South African Chenin Blanc wines made from the same source grapes under 3 conditions: control (no skin contact), skin contact before fermentation (ScBF), and full fermentation on the skins (FoS); evaluated by a descriptive-analysis panel.

Note: A source separate from the 2 existing claims (Sokolowsky 2015 and Mikayelyan 2026). It adds the condition dependence of the effect on bitterness according to whether skin contact occurs only briefly before fermentation or throughout fermentation (no significant difference for the former; a significant increase for the latter).

Scope: Layer: food. Chips from 40 persimmon cultivars; trained-panel descriptive analysis (4 taste attributes calibrated at 4 reference-concentration levels) and a PLSR regression model of preference rankings from more than 100 consumers.

Note: This source used hot-air drying, unlike the traditional peeled-fruit natural drying (sometimes with sulfur fumigation) addressed by the existing claim. Mean numerical bitterness intensity is not given in the main text, only in supplementary figures (Supplemental Figure S4), so the verbatim quotation is limited to the qualitative description.

Scope: Layer: solution. Capsaicin, menthol, sucrose, NaCl, citric acid, and QSO4 (quinine sulfate) were presented at the tongue tip (experiment 1) or both front and back of the tongue (experiment 2); intensity was rated on a Labeled Magnitude Scale. Participants were grouped as thermal tasters/non-tasters and by high/low sweetness sensitivity.

Scope: Layer: solution. Adult participants' ratings using a sip-and-spit method and the general Labeled Magnitude Scale.

Scope: Layer: solution. Ratings by the sip-and-spit method and the general Labeled Magnitude Scale.

Scope: Layer: food (pharmaceutical orally disintegrating tablets). A human sensory test using a VAS (visual analog scale).

Scope: Layer: Literature. A review on the interaction of pungent stimuli and basic tastes (sweet, sour, salty, bitter, umami).

Scope: Layer: Literature. A review on the interaction of pungent stimuli and basic tastes (sweet, sour, salty, bitter, umami).

Scope: Layer: Food. 10 Trigonella species, 30 accessions of leaves; principal component analysis (biplot) (Fig. 8a).

Scope: Layer: Literature. Introduction section summarizing prior research on bitter-tasting compounds in roasted coffee.

Scope: Layer: food (human sensory trial). Sequential tasting and bitterness ratings of real-drink pairs of chicory, surrogate coffee, and roasted coffee (panel of 16).

Scope: Layer: food (human sensory trial). Another pair in the same sequential-presentation study: surrogate coffee and roasted coffee.

Scope: Layer: literature (a description in a review).

Scope: Layer: literature (a description in a review).

Scope: Layer: Solution. Food-grade EGCG derived from green tea was dissolved in water (final concentration 0.2-0.8 mg/mL) and dispersed by sonication. Evaluated using 3-AFC and QDA methods (VAS, n=7).

Scope: Layer: Solution. Cocoa-derived procyanidin-rich fraction (PRF) was dissolved in water (final concentration 0.2-0.8 mg/mL) and dispersed by sonication. Evaluated using 3-AFC and QDA methods (VAS, n=7).

Scope: The expression that the Ministry of Agriculture, Forestry and Fisheries' 『うちの郷土料理』 (in translation: "Our Local Cuisine") gives for the flavor of the peel in Yamagata Prefecture

Scope: Schmidt et al. 2014, 12 trained panelists, a fresh Pilsener control, a 0–9 scale following triangle discrimination, fresh beer and beer stored at 28 °C for 2 and 4 months

Note: The chemical analysis was at 5/28 °C and 4/8/12 months, while the sensory testing was separate, at 28 °C and 2/4 months. Fresh-beer bitterness intensity was 5.8 for P90 and 6.0 for IPE. This does not support a causal claim that a higher cis/trans ratio improves sensory stability.

Scope: King and Duineveld 1999, 8 commercial lager brands, 26 samples, a trained panel of 16 women, 15 mL at 13±2 °C, squeezer time-intensity

Note: Each sample was tested sensorially 2 or more times, mostly 3 times. There were strong correlations among the 5 peaks, and other bitter compounds were also detected in some products, but these were excluded from the model because the analysis was incomplete. The decrease in trans concentration alone is not treated as the cause of the sensory decrease.

Scope: Layer: food. Human sensory evaluation using bitter gourd extract (a panel selected and trained in bitterness identification and ranking). An experiment (Figure 3) comparing salt, IMP, and MSG added individually as candidate active components for the bitterness suppression observed with katsuobushi stock.

Scope: Layer: food. A human sensory panel (n=7) using 4 commercial cheeses and beer. Baraka was selected through a preliminary screening of 71 cheese brands.

Note: The correspondence between the total free-fatty-acid concentration and masking activity is a descriptive trend across 4 samples, and the fatty-acid composition ratio itself was nearly the same among the 4 cheeses (all shared the feature that oleic acid, palmitic acid, myristic acid, and stearic acid accounted for 60% or more of total free fatty acids). Details of the 71-brand screening results themselves are in the Supporting Information, and the main text gives no figures.

Scope: Layer: solution (fractions of the cheese's oily extract; a mixture mimicking the cheese's fatty-acid composition). Human sensory evaluation (a method comparing against a 7-point scale of standard quinine solutions).

Note: The evaluation of the mixed fatty-acid solution had large variance among panelists (ANOVA F-test p=0.001). The authors cite the low solubility of the saturated fatty acids (myristic acid, palmitic acid, and stearic acid) as one cause. With oleic acid alone (0.5 mM), bitterness was suppressed down to the equivalent of 0.0032-0.0038%, and the variance among panelists was also small (F-test p=0.131) (a different part of the same experiment as the claim in the existing concept-taste-mixture-suppression entry).

Scope: A dynamic sensory evaluation of purple eggplant and zucchini boiled or baked for 15, 30 and 45 minutes (as described in the abstract). The abstract does not show which cooking conditions were bitter.

Note: A claim read from the abstract only. The abstract states that the longer chewing counts and eating times were in the baked samples and the briefly cooked samples, so the correspondence between bitterness and cooking method and time must be checked in the full text. If incorporated, do not generalize it as a relation between cooking time and bitterness.

Scope: Mineral water containing bitter gourd powder. 40 students and 23 teachers, 0 to 10 numerical scale. Friedman test followed by Wilcoxon signed-rank test (Holm correction). Open-label, with the samples presented to everyone in the same order (the effect of order was not separated)

Note: This was a test in which bitter gourd powder was mixed into water of different temperatures, not the effect of cooling or warming a dish. Open-label. The effect of temperature was seen only in the students and not in the adults (teachers). The result does not agree in direction with the study in which grapefruit juice at 60°C was more bitter than at 10°C (Morishita et al. 1989), where higher temperature meant more bitter (here, cold water was bitter too). The values are not in the text but only in Figure 3.

Scope: Human oral bitterness perception

Note: Do not fix the receptor count without a current nomenclature source. / 2026-08-31: Calibration downgrade from established to supported, because the supporting evidence does not derive from a full-text check. Can be re-upgraded after a full-text check.

Scope: Caffeine's experimental use as a bitter stimulus

Note: The review in question also discusses receptor-independent pathways in addition to the canonical pathway.

Scope: The role of the galloyl group is inferred from the hTAS2R39 response order (ECg, EGCg >> EC, EGC), described as resembling human taste-intensity observations.

Note: A direct human dose-response is not part of this assay. The human comparison in the receptor study is a citation, not something the study itself carried out.

Scope: Salivary protein measured in the study in which EGCG was taken repeatedly for 2 weeks

Note: The change in perceived bitterness intensity and the change in salivary protein did not correspond one to one.

Scope: Chapter 7 (the chemistry of coffee's taste) of the SCA's official Coffee Sensory and Cupping Handbook (2021)

Note: Original text: "Sourness is preponderant in light roasts and bitterness in dark roasts." "bitterness actually increases with the roast level". It explicitly states that caffeine is only one part of coffee's bitterness compounds, and that bitterness increases even though caffeine decreases with roasting ("caffeine ... only accounts for a small percentage of coffee's bitterness").

Scope: Layer: cell. A cell-based assay using cells expressing human taste receptors.

Scope: Layer: cells. Effect of adding glycated beef protein hydrolysate to a quinine-stimulated cell assay (Fluo-4 NW calcium-mobilization assay).

Note: Alongside reduced bitterness measured by electronic tongue, the quinine-induced calcium response was inhibited at the cell level.

Scope: Layer: Literature (review citing previously reported GC-MS analysis results in a speculative statement).

Note: Original review phrasing is 'might be contributing' (hedged). Do not alter to a definitive claim.

Scope: Layer: cell (receptor-level explanation); literature (description in a review).

Scope: Horie 2011 (Journal of Cookery Science of Japan 44(6):407-410), Table 2 and the main text on p.409. The control is Table 1, p.408 (chewed with water alone, n=4)

Scope: Processing of table olives

Note: Method and final residual bitterness vary by product style. / 2026-08-31: Recalibrated from established to supported, because the supporting evidence does not derive from a full-text check. May be re-upgraded after a full-text check.

Scope: Formed preferentially at light-to-medium roast. At heavy roast it decomposes, generating harsh-bitter 4-vinylcatechol oligomers

Note: The chemical basis for how the bitterness signature of coffee changes with roast degree and extraction conditions.

Scope: Formed under heavy-roast conditions alongside the decomposition of quinides, producing a harsh bitterness quality

Note: The chemical substance behind how the “quality” of bitterness changes with roast degree.

Scope: Green tea extracted at 85-95 C for 30-45 minutes. Taste scores fell to 1.7 (85 C, 45 minutes) and 0.1 (95 C, 45 minutes) on a 0-10 scale, attributed by the panel to perceived bitterness. EGCG itself peaked early (50.69 mg/100 ml at 85 C, 3 minutes) and then declined.

Note: The trained panel of n=9 rated acceptability, not bitterness intensity directly. The paper does not attribute bitterness after prolonged extraction to a specific compound.

Scope: 27 roasting treatments across 3 origins, 145 chocolate consumers, gLMS

Note: The direction is the reverse of the intuition that 「焙煎温度が高いほど苦くなる」 (in translation: "the higher the roasting temperature, the more bitter it becomes"). No p-value is given for this effect size.

Scope: trans-specific conversion products formed during beer aging. Quantified in stored commercial beer

Note: Explains the change in the quality (not only intensity) of beer bitterness with storage. The threshold range given in the abstract is for the compound set, not per-compound values.

Scope: 4 washing conditions for freshly-cut witloof chicory

Note: Warm-water treatment reduced total sesquiterpene lactones by 60.9-64.5%.

Scope: A literature synthesis on the timing of hop additions in beer brewing

Note: The background is the isomerization of alpha acids during the boil. This is contextual because it is a literature synthesis in the introduction, not a direct comparison from the main experiment.

Scope: Unsweetened (100%) chocolate, 3 cacao origins (Ghana, Madagascar, Peru), gLMS sensory evaluation by a consumer panel of 145

Note: The source reports that bitterness on the gLMS scale fell by an average of about 1.56 units for every 42°C rise in roasting temperature. The size of the decline varied by origin: a drop of about 8 points for Ghana, about 2.4 points for Madagascar, and about 3 points for Peru is reported. The subject is unsweetened chocolate, and extrapolation to sweetened milk chocolate cannot be confirmed from this study.

Scope: Experimental brewing in which 3 hop varieties — Aurora, Celeia, and Styrian Wolf (storage index 0.3-0.7) — were added to the wort boil at 5, 45, and 90 minutes

Scope: Layer: Food. Comparison of Kao Nampung pomelo mesocarp powder treated with ultrasound alone (β-CD concentration 0%, 0CyUAP) and untreated powder (PPA).

Note: The reduction in bitterness with ultrasound alone, without complex formation, offers a different perspective from the existing claim about the combined effect of β-CD and ultrasound.

Scope: Layer: Literature. Background description of the pathway by which quinide compounds are generated from chlorogenic acids in roasted coffee.

Scope: Layer: Literature. Background description of the formation pathway from quinides to 4-vinylcatechol oligomers (phenylindanes) in roasted coffee.

Scope: Layer: food. Sesame (Sesamum indicum) protein. A simplex-lattice mixture design, with bitterness value measured by an E-tongue (TS-500Z, bitterness sensor C00).

Note: An example in which adding Flavourzyme, whose activity is mainly exopeptidase, acts to reduce bitterness. The text explains that the Alcalase-alone condition is on the more-bitter side because of exposed hydrophobic residues.

Scope: Layer: recipe (an introduction by a cook). Not a sensory experiment. Posted on the Japan Umami Seasoning Association's recipe site (Seiko Ogawa, 2020-04-02).

Note: What the original text explicitly links is the combination of 「クレソンの苦味」 (in translation: "the bitterness of the watercress") and 「アーモンドの香ばしさ」 (in translation: "the toasty aroma of the almonds"), and there is no direct statement that the cheese weakened the bitterness of the watercress. The role of the cheese is explained in the introduction as a substitute for salt and umami so the dish can be finished without added salt. This is recorded as the cook's practical knowledge, not as sensory data demonstrating the interaction of bitterness and umami.

Scope: Layer: recipe (an introduction by an instructor). Not a sensory experiment.

Note: This is a dressed dish involving salt-boiling, rinsing in water, ground sesame, soy sauce, and sugar, and is not a comparison isolating the cheese alone. The assessment 「まろやかにしてくれます」 (in translation: "mellows it") is stated by the instructor as a composite impression that includes the cheese's saltiness, umami, and fat content, and is not an experiment that measured the interaction of bitterness and umami.

Scope: IOC COI/T.20/Doc.15/Rev.11 (Italian edition, June 2024), sections 4.1-4.3.

Scope: OIV's ‘Sensory Analysis of Wine’ document (March 2016), Part I b), the section on tests for judging sensory acuity. Covers the sensory panel training program for grapes and grape-derived beverages (moûts, vins et autres boissons d'origine vitivinicole).

Note: The same section lists the five basic tastes to be checked in stimulus-detection training as ‘sweet, sour, salty, umami, bitter,’ with astringency (astringence) appended alongside it in a separate category, as "ainsi que" (in addition). The document’s own opening Avertissement states that it has not gone through the member-state resolution review procedure and "cannot be treated as an OIV resolution," being a subcommittee consensus document instead — so this claim is recorded as a record of institutional positioning, not a claim of established scientific consensus.

Scope: Part I, Table 1 of the same document. A table of guideline reference-solution concentrations used to train candidate sensory panelists in stimulus detection.

Note: In the alternative ISO 3972 table accompanying the same table, caffeine at 0.195 mg/L (the concentration detected and identified by 50% of novice subjects) is separately listed as the bitterness identification criterion.

Scope: Part III, section 3, and the attached evaluation form of the same document, on selecting and training a panel to evaluate visual, olfactory, tactile, and gustatory alterations in still red, white, and rosé wines.

Note: That section classifies the principal fault attributes of still red, white, and rosé wines into 3 groups: 『匂いの系統』 (in translation: "odor families"), 『味（酸味・苦味）』 (in translation: "taste (sourness and bitterness)"), and 『触感（渋味）』 (in translation: "tactile sensation (astringency)"). The attached 0–5 rating form also lists 『酸味・苦味』 (in translation: "sourness and bitterness") under taste (GUSTATIVES) and 『渋味』 (in translation: "astringency") separately under tactile sensations (TACTILES). This is included as a further confirmation that bitterness and astringency are treated separately, in a different section and context from Part I, which trains panelists on basic tastes.

Scope: The "QUALITE GOUT" (taste quality) description field of the 100-point scoring sheet in RÉSOLUTION OIV/CONCOURS 332A/2009 (the standard for the International Wine and Spirits Competition, formally adopted as a resolution by member states).

Note: This description field lists, as components of the "richness" (richesse) of flavour felt in the mouth: aromatic complexity, structure (acidity, tannin, alcohol), coating elements (fattiness), residual sugar, and bitterness (amertume). Bitterness is listed here as a separate item from tannin. Note that the same OIV's 2016 sensory analysis document explicitly states that "concours are excluded from the scope of this document," so the treatment under this concours standard is not equated with OIV's sensory analysis methodology itself.

Scope: The recorded Lisu dish name and preparation are presented explicitly as Tom Khom, that is, a bitter soup

Note: Even recipes sharing the same name can differ in bittering ingredient and intensity.

Scope: As above.

Note: Descriptions of the bitterness differ by source: one describes a shift from bitterness to sweetness, “刚入口时虽苦，但紧随而来的是爽口的甘甜” (in translation: "bitter at first, but immediately followed by a refreshing sweetness"), and another describes a bitter-pungent-fragrant sequence, “先苦，再辣，然后是牛肉的香” (in translation: "bitter first, then pungent, then the aroma of beef"). The intensity or mechanism of the bitterness is not generalized.

Scope: As above.

Note: Sources share a common description in which bitterness gives way to a fatty sweetness (“vị đắng ban đầu nhanh chóng chuyển sang vị béo ngậy, ngọt bùi đặc trưng”, in translation: "the initial bitterness quickly turns into a distinctive rich, fatty sweetness"). An academic journal article likewise states “có vị đắng” (in translation: "has a bitter taste").

Scope: An interview article in beverage-industry media.

Note: Sother Teague (Beverage Director, Overthrow Hospitality / Amor y Amargo, New York) is quoted as saying “for me the defining characteristic of a digestive is an obvious bitter quality”. Attribution records his name, role, and restaurant as stated in the article. This is an individual industry participant's statement, not a claim by NIGAMI LAB.

Scope: Sierra Nevada Brewing Co.'s official product page, Torpedo Extra IPA (a differentiated craft IPA brand)

Note: The STATS block on the official page displays "bitterness units (IBU): 65" as a headline figure alongside ABV, calories, and the like, and the tagline reads "The original 'Extra' IPA delivers a direct hit of hops, every time." A primary source showing a differentiated brand putting the IBU figure itself at the front of its product appeal.

Scope: Layer: literature (a review's secondhand account of an ancient text).

Scope: Layer: literature (a description in a review).

Scope: Layer: literature. Ethnobotanical field study through semi-structured interviews with 31 residents of Ikaria, Greece.

Note: The same source is also used for another generalized claim concerning the whole Ikaria survey (such as the proportion of wild leafy vegetables identified as bitter), but this claim concerns the individual record row for Cichorium spinosum (part, cooking method, taste classification, and frequency of mention).

Scope: Layer: Literature. A mini-review of ethnopharmacological and nutritional literature on Gongronema latifolium in West Africa (mainly Nigeria), based on PubMed and Google Scholar searches.

Note: This account cites Adelaja and Fasidi (2009) and Osuagwu et al. (2013) as its sources in the review text. Because it is not a primary measurement by the review authors, claim_status was set to preliminary.