Topic hub — 2026-10-21
Does onion turn bitter when sautéed for a long time?
Sauté onion until golden brown and it turns sweet; overdo it and it turns bitter: cooking articles often warn of this. What do studies in which people actually tasted sautéed onion say about time and bitterness? This page lines up the included studies together with their conditions: the cut and amount, the pan and heat, the sautéing time, the form tasted, and who rated it on what scale. It then separates what was established within one experiment, what differences between studies might explain, and what this comparison alone cannot separate.
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 full papers do report bitterness appearing with long sautéing, in each case at about the same time as a burnt odour or scorched colour.
- That how many minutes it took differed greatly between studies, and which difference in conditions explains this has not been tested.
- That in one comparison, soup with briefly fried onion was more bitter than soup with onion sautéed far longer, so time alone does not decide it.
- That the mechanism, and the compounds responsible, have not been established in the heating studies.
What the included studies allow us to say
- 2 full papers report bitterness appearing with long sautéing. In one, with 1 mm slices in an electric pan, at least 7 of 9 people sensed bitterness only at 60, 65 and 70 min; in the other, with diced onion on low heat in an iron pan, slight bitterness was described at 10 min. In both it came at about the same time as a burnt odour or scorched colour. The 2 differ in cut, amount, pan, heat, fat and rating method, and which of these explains the different times has not been tested. [rows: Tamaki & Ukai 2003 sautéed onion; Shimada 1966 diced, sautéed in oil]
- It cannot be said to depend on time alone: soups with onion sautéed 165 min in butter were less bitter than soup with fried onion (10 min). The mechanism by which long sautéing turns onion bitter, and the compounds responsible, have not been established in the heating studies in this table. [rows: Shibata 2004 fried vs sautéed (soup); Tamaki & Ukai 2003 sautéed onion; Shimada 1966 diced, sautéed in oil]
Bitterness ratings at a glance
Only the results in which people rated bitterness. Values for "Sample compared" and "Comparison" are as reported in the tables or figures (values read from figures are marked as estimates). "Direction" is the larger of the two values; gaps the paper does not treat as a difference are shown as "about the same". Select a study name to jump to its detailed table.
Results in which people rated bitterness only. Values are as reported; scales and methods differ between studies, so compare within a row, not across rows.
| Study | Condition | Measured as | Sample compared | Comparison | Direction / test |
|---|---|---|---|---|---|
| Tamaki & Ukai 2003 | Sautéed 60, 65 and 70 min vs 1–55 min | whether at least 7 of 9 judged it present | bitterness marked | not marked | Sample compared higher No test of the difference |
| Tamaki & Ukai 2003 | Soups from onion sautéed 60, 65 and 70 min vs shorter times | whether at least 7 of 9 judged it present | bitterness marked | not marked | Sample compared higher No test of the difference |
| Shimada 1966 | 10 min on low heat vs 2, 5 and 8 min (the times described in the table) | verbal description | rich sweetness with slight bitterness | no bitterness described | Sample compared higher No test of the difference |
| Shibata 2004 | Soup with fried onion (120 °C, 10 min) vs 5 soups with sautéed onion (165 min) | mean on a 7-point scale (13 people, estimated from the figure) | about 4.0 | about 2.4–2.7 | Sample compared higher Tested, significant |
| Tamaki 2002 | 12 cultivars sautéed about 20 min vs Sarari | −2 to +2 (negative = more bitter; 12 people; estimated from the figure) | most on the bitter side (about −1.5 to −0.2) | 0 (Sarari) | Sample compared higher Tested, only some pairs significant |
Conditions and results, study by study
For each study, the conditions for the onion, the cooking, the form tasted and the rating, 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 longer or harder cooking brings out bitterness, with the reason. Nothing is left blank: "not given", "not read" and "not applicable" are kept apart.
Tamaki & Ukai 2003 sensory only
長時間炒めたタマネギの味, 香り, 遊離糖, 色の変化. 日本家政学会誌 54(1):69-76 — doi:10.11428/jhej1987.54.69
- How deeply checked
- Checked in full text — Read in the full text of the J-STAGE PDF (Table 1, Figs 2–4); the marks in Table 1 were read from the image
- Samples
- One yellow cultivar from Hokkaido, Kitamomiji (store-bought); sliced lengthwise about 1 mm thick, 200 g per batch
- Roasting
- Electric pan with 20 g soybean oil (10% of the onion), preheated 5 min; high heat for the first 5 min (250 °C in the text, 230 °C in the figure notes), then low heat at 170 °C, stirring; 1–5 min and then every 5 min up to 70 min (18 samples)
- Brewing
- The sautéed onion, and a soup of one quarter of it (equivalent to 50 g raw) with 200 mL distilled water, simmered 10 min after boiling with evaporated water replaced (solids removed); served at room temperature
- Who rated, on what scale
- 9 trained food-science lab members judged, from the shortest time onward, whether each attribute was present; attributes noted by at least 7 of 9 were marked; the 3 most preferred, sweetest and tastiest samples were each chosen; neither an intensity scale nor a statistical test; number of preparation replicates not given
| Measured | Condition | Sample compared | Comparison | Unit | Direction / test |
|---|---|---|---|---|---|
| Bitterness intensity (sensory) | Sautéed 60, 65 and 70 min vs 1–55 min | bitterness marked | not marked | whether at least 7 of 9 judged it present | Sample compared higher No test of the difference |
| No test; no mark means the threshold was not reached, not that nobody sensed bitterness; burnt odour from 55 min, dark-brown colour from 60 min Where: Table 1, p. 71 For whether longer or harder cooking brings out bitterness: Limited — The same 9 people compared only the sautéing time; but it is a presence judgement with no test, for one cultivar, thin slices and an electric pan, and the number of preparation replicates is not given | |||||
| Bitterness intensity (sensory) | Soups from onion sautéed 60, 65 and 70 min vs shorter times | bitterness marked | not marked | whether at least 7 of 9 judged it present | Sample compared higher No test of the difference |
| No test; burnt odour in the soup only at 70 min; the soups judged best were from 50–60 min (read from the mark positions) Where: Table 1, p. 71 For whether longer or harder cooking brings out bitterness: Limited — As above; diluted as soup | |||||
Shimada 1966 sensory only
タマネギの調理に関する研究 (第1報). 家政学雑誌 17(1):389-394 — doi:10.11428/jhej1951.17.389
- How deeply checked
- Checked in full text — Read in the full text of the J-STAGE PDF (Figs 1–3, Table 4) as images; pan temperatures estimated from the figures
- Samples
- Yellow onion from Senshu (printed as "ki-chūsei" in the source); diced about 4 mm, 100 g per batch
- Roasting
- Iron frying pan (24 cm across, 18 cm base) on low heat (one third of full gas); onion added when the pan bottom was about 120 °C and stirred 70–80 times a minute; 2–10 min (9 steps); soybean oil, salad oil or margarine at 5, 7, 10 or 15% of the onion; pan bottom about 150–190 °C at 10 min (estimated from the figures; varies with fat type and amount)
- Brewing
- The sautéed onion (tasting temperature and method not given)
- Who rated, on what scale
- A table describing state, colour, aroma and taste in words; who rated, how many, the scale and statistics are not given
| Measured | Condition | Sample compared | Comparison | Unit | Direction / test |
|---|---|---|---|---|---|
| Bitterness intensity (sensory) | 10 min on low heat vs 2, 5 and 8 min (the times described in the table) | rich sweetness with slight bitterness | no bitterness described | verbal description | Sample compared higher No test of the difference |
| Panel, method and tests not given; the table is not split by fat type or amount; at 10 min small pieces scorched and faint smoke rose Where: Table 4, p. 394 For whether longer or harder cooking brings out bitterness: Limited — Descriptions of samples at different times, but fat type and amount were also varied and the table does not say which condition it shows; the rating method is not described either | |||||
Shibata 2004 sensory only
オニオンスープの食味および呈味成分に及ぼすコンソメ類と炒めタマネギの影響. 日本家政学会誌 55(5):389-398 — doi:10.11428/jhej1987.55.389
- How deeply checked
- Checked in full text — Read in the full text of the J-STAGE PDF (Tables 1, 2 and 4, Fig. 6); Fig. 6 values estimated from the figure
- Samples
- Sliced onion, cultivar Momiji No. 3 from Awaji Island; prepared by a chef
- Roasting
- Sautéed: 15 kg in unsalted butter (0.8% of raw) on high then medium heat, 165 min in total, yield 18.5% / fried: 400 g in 8 times its weight of salad oil (preheated to 160 °C) at 120 °C for 10 min, yield 22.5%; amount, fat, time and temperature differ at once; the sautéing temperature is not given
- Brewing
- 900 g of base with 150 g sautéed or 100 g fried onion (17% and 9% in the text; 11% for fried when calculated from Table 1; adjusted by the chef to give a similar finish, so raw-equivalent amounts differ); simmered about 6 min, salted to 0.5%, served at 80 °C; sautéed onion in 5 bases, fried onion in instant beef stock
- Who rated, on what scale
- 13 cookery staff at a university (women aged 20–60); 7-point scoring; ANOVA with Bonferroni multiple comparisons; training and replicates not given
| Measured | Condition | Sample compared | Comparison | Unit | Direction / test |
|---|---|---|---|---|---|
| Bitterness intensity (sensory) | Soup with fried onion (120 °C, 10 min) vs 5 soups with sautéed onion (165 min) | about 4.0 | about 2.4–2.7 | mean on a 7-point scale (13 people, estimated from the figure) | Sample compared higher Tested, significant |
| Only the fried-onion soup was significantly more bitter (1% level); the sautéed onion was cooked far longer, yet its soups were less bitter; 4 of the 5 also used a different base; liking of bitterness showed no significant difference Where: Fig. 6, p. 397 For whether longer or harder cooking brings out bitterness: Limited — People compared soups with a test, but heating method, time, fat, batch size, the proportion added and mostly the base differ at once; it is not a comparison of sautéing time | |||||
Tamaki 2002 sensory only
北海道産タマネギの品質と調理加工特性. 日本食品保蔵科学会誌 28(6):291-298 — doi:10.5891/jafps.28.291
- How deeply checked
- Checked in full text — Read in the full text of the J-STAGE PDF (Fig. 6 and text); cultivar positions in Fig. 6 estimated from the figure
- Samples
- 13 Hokkaido cultivars (12 yellow, 1 red); before cold storage, at least 5 bulbs mixed, sliced about 1 mm, 200 g
- Roasting
- Electric pan with 20 g soybean salad oil preheated 5 min to about 160 °C; high heat for the first 5 min (pan dial 250 °C) then low heat at 170 °C, about 20 min until the weight including oil fell to 84 g (the time judged sweetest in a pilot)
- Brewing
- The sautéed onion at room temperature, 3 samples per session
- Who rated, on what scale
- 12 trained junior-college lab members (women aged 19–20); 5-point scale from −2 to +2 against the cultivar Sarari as 0 each time; two-way ANOVA and Tukey test
| Measured | Condition | Sample compared | Comparison | Unit | Direction / test |
|---|---|---|---|---|---|
| Bitterness intensity (sensory) | 12 cultivars sautéed about 20 min vs Sarari | most on the bitter side (about −1.5 to −0.2) | 0 (Sarari) | −2 to +2 (negative = more bitter; 12 people; estimated from the figure) | Sample compared higher Tested, only some pairs significant |
| The figure marks significant differences from Sarari (5% level); those for Kamui, Sorachiki and Kurenai can be read, others overlap and could not be confirmed; in yellow onions, more total phenolics went with more bitterness (r=0.631, p<0.1) Where: Fig. 6 and text, p. 297 For whether longer or harder cooking brings out bitterness: Not usable — A comparison between cultivars; sautéing time was not varied | |||||
What was established within an experiment
Only results where the same panel compared changed conditions within one study.
- With the same pan and heat and only the time changed, bitterness was marked only at 60, 65 and 70 min for both the onion and its soup (at least 7 of 9 people; no test); burnt odour appeared in the sautéed onion from 55 min (in the soup only at 70 min). [rows: Tamaki & Ukai 2003 sautéed onion; Tamaki & Ukai 2003 soup]
- Diced onion sautéed on low heat had scorched pieces and slight bitterness at 10 min (the rating method is not described). [rows: Shimada 1966 diced, sautéed in oil]
- In ratings by 13 people, soup with fried onion (about 4.0) was significantly more bitter than the 5 soups with sautéed onion (about 2.4–2.7); but several conditions differed at once between frying and sautéing. [rows: Shibata 2004 fried vs sautéed (soup)]
Candidate explanations for the differences
Conditions that differ between studies, or between ways of cooking, and could explain differences in bitterness. Several conditions differ at once, so which one mattered is unknown. These are candidates, not causes.
- Scorching and browning. Bitterness appeared at about the same time as burnt odour and scorched colour, and the authors suggest charring of sugars and pieces (1966) or browning reactions (2004); both are the authors' inferences, and no product responsible for the bitterness was identified (the 2004 study measured a correlation between bitterness and soup colour but did not separate cause). [rows: Tamaki & Ukai 2003 sautéed onion; Shimada 1966 diced, sautéed in oil; Shibata 2004 fried vs sautéed (soup)]
- Cooking temperature or how heat is applied. Soup with onion fried for only 10 min was more bitter than with sautéed onion, and bitterness appeared at 10 min once the pan bottom had heated up on low heat. Temperature or heat exposure may be involved, but in the studies in this table time and temperature changed together and none separated them (one study does not give the sautéing temperature). [rows: Shibata 2004 fried vs sautéed (soup); Shimada 1966 diced, sautéed in oil]
- Cultivar. With the same sautéing, bitterness differed by cultivar, and among yellow onions those higher in phenolics tended to be more bitter (r=0.631, p<0.1; not significant at the 5% level, and not evidence of cause). [rows: Tamaki 2002 cultivars (sautéed about 20 min)]
What is not known — what this comparison alone cannot separate
- Time and scorching: the long-sautéed samples were also scorched, so whether bitterness appears with long sautéing without scorching cannot be separated. [rows: Tamaki & Ukai 2003 sautéed onion; Shimada 1966 diced, sautéed in oil]
- Strength of bitterness: the 60-minute study judged presence and the 10-minute study gave verbal descriptions, so whether weak bitterness was already present at shorter times is unknown (the same lab's cultivar comparison rated most cultivars sautéed about 20 min as more bitter than the reference cultivar, but that is a comparison between cultivars, not a judgement of whether bitterness appeared). [rows: Tamaki & Ukai 2003 sautéed onion; Shimada 1966 diced, sautéed in oil; Tamaki 2002 cultivars (sautéed about 20 min)]
- Frying versus sautéing: heating method, time, fat, batch size, the proportion added to the soup and mostly the soup base all differ, so which one separated the bitterness is unknown. [rows: Shibata 2004 fried vs sautéed (soup)]
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.
- Sources in the table: 4, of which 4 had people rate bitterness; the others measured something else (compounds, smell) or are used only for context.
- Rows in the table (study × measured result): 5. Rows on perceived bitterness: 5.
- 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.
- Independent research groups among the sensory studies: 3 (reports from the same lab count as 1).
What we looked at
The sources examined for this question, why each was included or excluded, and which full texts could not be reached. We searched J-STAGE, CiNii and PubMed for studies on onion bitterness and sautéing, frying, heating, scorching or soaking in water, and added the sources already in the lab's ledger. In the sources searched, no study was found in which people compared the bitterness or pungency of raw onion before and after soaking in water.
| Source | Decision | Why |
|---|---|---|
| 長時間炒めたタマネギの味, 香り, 遊離糖, 色の変化 (2003) doi | Included in the table | People rated samples differing only in sautéing time; read in full |
| タマネギの調理に関する研究 (第1報) (1966) doi | Included in the table | A table of observations at different sautéing times; the rating method is not described, but it is one of few full texts linking time and bitterness |
| オニオンスープの食味および呈味成分に及ぼすコンソメ類と炒めタマネギの影響 (2004) doi | Included in the table | People compared the bitterness of soups with fried and sautéed onion, with a test; read in full |
| 北海道産タマネギの品質と調理加工特性 (2002) doi | Included in the table | Time was not varied, but it shows cultivar differences in bitterness under the same sautéing; read in full |
| Allithiolanes: Nine Groups of a Newly Discovered Family of Sulfur Compounds Responsible for the Bitter Off-Taste of Processed Onion (2018) doi | Read as context (not an experiment) | Found bitter sulfur compounds in processed onion; abstract only, and which processing forms them is unknown |
| 北海道産玉ねぎを使用したオニオンソテーの品質評価 (2010) doi | Read as context (not an experiment) | Cultivar comparison of sautés cooked to different degrees; abstract only, with no bitterness by degree of cooking |
| Taste intensities of ten vegetables commonly consumed in the Netherlands (2016) doi | Full text not reachable | Taste intensities including raw and cooked onion; abstract only, with no onion cooking method or bitterness values in it |
| （生の玉ねぎを水にさらす前後で人が苦味や辛味を比べた研究） | Excluded | Not found in the searches of J-STAGE, CiNii and PubMed (which does not show that none exists) |
Read in the encyclopedia
- Onion — the vegetable in this question
- Onion preparation — preparations such as sautéing and frying that change bitterness (Japanese page)
Source ledger
Each study's source can be reached from its section above. All of the lab's sources are listed in thesource ledger.
How to cite this page
Aoki, M. (NIGAMI LAB) (2026). Does onion turn bitter when sautéed for a long time?. https://nigamilab.com/en/topics/onion-long-saute/
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