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Topic hub — 2026-10-22

Does beer's bitterness change as it ages in the bottle or can?

A caveat first: few studies in which people compared the bitterness of the same beer stored for different times or at different temperatures could be checked down to their conditions in full text. The included studies found both weaker bitterness after longer storage and, under refrigeration, equal median bitterness scores at the start and end with no significant difference detected. Storage temperature and duration, the beers (trial or commercial) and the scales all differ by study, so it cannot be said across studies how much bitterness changes in how many months. The point of this page lies in that limit. BU, measured by instrument, and the bitterness people perceive are read apart, as are bitterness intensity and bitterness quality such as a lingering bitter aftertaste. All tabled rows are bottled beer; no study comparing cans with bottles is in the table. This page lines up the included studies together with their conditions: the beers, storage, how they were served, and who rated them on what scale. It then separates what was established within one experiment, what differences might explain, and what this comparison alone cannot separate. It is about perceived taste, not guidance on best-before dates or on choosing or drinking beer. The relation between IBU and bitterness is covered on the IBU and bitterness page.

What this page establishes

• That some studies reported weaker perceived bitterness after longer storage of the same beer, while another found equal median bitterness scores at the start and end of refrigerated storage with no significant difference detected, which does not show that there is no difference.
• That the studies in which bitterness fell include samples aged quickly at high temperature and values pooled over temperatures and addition levels, and that one reports no test.
• That while instrumental BU fell with storage temperature, the effect of temperature on perceived bitterness in the same experiment was not significant, so perceived bitterness and BU are read apart.
• That the only row comparing the intensity of bitter aftertaste, an attribute related to bitterness quality, before and after storage has a table and discussion that disagree on significance, so it cannot be established as a significant storage effect.
• That storage temperature, duration, beers and scales differ by study, so it cannot be said across studies how bitterness changes over how many months.

What the included studies allow us to say

• Studies in which people compared the bitterness of the same beer stored for different times found both weaker bitterness after longer storage and, under refrigeration, equal median bitterness scores at the start and after 6 months with no significant difference detected. In a trial lager in brown bottles stored at 3–35 °C (Pangborn et al. 1977), mean bitterness pooled over temperatures and addition levels fell from 2.69 to 1.92 between the median days 6 and 132 of the evaluation periods, and the effect of time was significant. In a commercial lager kept at 30 °C for 12 weeks (Wu et al. 2011), it fell from 6.6 to 3.1, with no test reported. In lagers in brown bottles refrigerated at 4 °C (Salek et al. 2022), the median bitterness scores at the start and after 6 months were both 3 for all 4 beers, with no significant difference detected, but there were 2 rises marked as significant in intermediate months. [rows: Pangborn 1977 Stored 132 days vs 6 days (median day of the evaluation period); Wu 2011 30 °C for 12 weeks vs fresh (kept at 4 °C); Salek 2022 Stored 6 months vs 0 months (all 4 beers; equal medians); Salek 2022 Stored 1 month vs 0 months (original wort extract 11.0%); Salek 2022 Stored 4 months vs 0 months (original wort extract 11.5%)]
• Storage temperature and time, the beers, containers and scales differ by study, so it cannot be said across studies how much bitterness changes in how many months. On storage temperature, within the experiment of Pangborn et al. the main effect of the 4 temperatures on perceived bitterness was not significant (F=0.209), while BU, measured by instrument, was lower at higher temperature (16.7 and 14.4). Perceived bitterness and BU are read separately. This page does not give guidance on best-before dates or on how to drink beer. [rows: Pangborn 1977 Stored at 35 °C vs 3 °C (pooled over time)]
• Only 1 row compares the intensity of an aftertaste related to bitterness quality before and after storage, and its table and discussion disagree on significance. In the experiment of Pangborn et al. storing a commercial lager for 6 weeks, bitter aftertaste went from 3.4 to 3.6 (15 °C) and 3.4 (25 °C); the table has no significance mark for storage, but the discussion says it increased significantly during storage, so it cannot be established as a significant storage effect. Bitterness intensity went from 4.0 to 4.1 and 4.2, with no significance mark. [rows: Pangborn 1977 Stored 6 weeks (15 °C) vs before storage (bitter aftertaste; table and discussion disagree on significance); Pangborn 1977 Stored 6 weeks (25 °C) vs before storage (bitterness)]

Bitterness ratings at a glance

Human bitterness ratings only. Beers, storage conditions and scales differ by study (ratios to a control for a trial lager, scores for a commercial lager, medians on a short scale for refrigerated lagers), so values are not compared across studies. The "Direction" column shows which sample was more bitter ("... more bitter"); in every row on this page the larger value is the more bitter one. The direction shows which published mean or median is larger, and 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. Rows where no significant difference was detected and rows with no test reported are kept as they are. The bitter aftertaste row rates the intensity of an aftertaste related to bitterness quality rather than bitterness intensity, and its label and note say that the table and discussion disagree on significance. Select a study name to jump to its 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.

Conditions and results, study by study

For each study, the conditions for the beers, storage, serving 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 the storage time or temperature of packaged beer changes the intensity or quality of the bitterness people perceive, with the reason. Nothing is left blank: "not given", "not read" and "not applicable" are kept apart.

What was established within an experiment

Only results observed in comparisons within one study. Perceived bitterness and BU are kept apart.

• When the same trial lager brew was stored, mean perceived bitterness pooled over temperatures and addition levels fell 2.69, 2.38, 2.37, 1.98 and 1.92 at median days 6, 36, 76, 97 and 132 of the evaluation periods, and the main effect of time was significant (F=41.591, p<0.001). By the LSD underlines in the table, 6, 36 and 76 days formed one group and 97 and 132 days another. BU in the same pooling went from 17.1 to 14.9. [rows: Pangborn 1977 Stored 132 days vs 6 days (median day of the evaluation period)]
• In the same experiment, mean perceived bitterness of samples stored at 3, 15, 25 and 35 °C was 2.16, 2.16, 2.14 and 2.18, and the main effect of temperature was not significant (F=0.209). BU was 16.7, 16.0, 15.4 and 14.4, lower at higher temperature, and the main effect of temperature was significant (F=216.246). [rows: Pangborn 1977 Stored at 35 °C vs 3 °C (pooled over time)]
• For the same commercial lager, bitterness was 6.6 ± 0.5 for the fresh beer kept at 4 °C and 3.1 ± 0.4 after 12 weeks at 30 °C. No test is reported for bitterness, and the type of ± is not stated. [rows: Wu 2011 30 °C for 12 weeks vs fresh (kept at 4 °C)]
• For the 4 lagers stored refrigerated (4 ± 2 °C), the median bitterness was 3 at both month 0 and month 6, with the same letters. Only the 11.0% original wort extract beer at month 1 and the 11.5% beer at month 4 were 4, marked as significantly different from month 0, and later months returned to 3. [rows: Salek 2022 Stored 6 months vs 0 months (all 4 beers; equal medians); Salek 2022 Stored 1 month vs 0 months (original wort extract 11.0%); Salek 2022 Stored 4 months vs 0 months (original wort extract 11.5%)]

Candidate explanations for the differences

Conditions that differ between studies and could explain the differences in bitterness results, and the authors' interpretations. Several conditions differ at once, so which one mattered is unknown. These are candidates, not causes.

• A candidate explanation for the differences between studies is storage temperature: bitterness fell in the study that kept beer at 30 °C for 12 weeks (Wu et al.) and in the one that stored it at 3–35 °C with the final evaluation period centred on day 132 (Pangborn et al.), while under 4 °C refrigeration (Salek et al.) median bitterness scores at the start and after 6 months were equal with no significant difference detected. Salek et al. cite an earlier report that degradation products of iso-alpha acids are hard to perceive during cold storage. However, within the experiment of Pangborn et al. the main effect of temperature was not significant, and between studies the beers, durations and scales also differ at once, so whether temperature explains this has not been confirmed. [rows: Wu 2011 30 °C for 12 weeks vs fresh (kept at 4 °C); Pangborn 1977 Stored 132 days vs 6 days (median day of the evaluation period); Pangborn 1977 Stored at 35 °C vs 3 °C (pooled over time); Salek 2022 Stored 6 months vs 0 months (all 4 beers; equal medians)]
• In their discussion, Pangborn et al. interpret storage as losing the bitterness tied to BU and replacing it with a bitterness of a different quality unrelated to BU, and propose that beer bitterness has at least 2 dimensions, intensity and quality. This is the authors' interpretation; the only values that rate the intensity of an aftertaste related to quality are in the bitter aftertaste row, whose table and discussion disagree on significance. [rows: Pangborn 1977 Stored 132 days vs 6 days (median day of the evaluation period); Pangborn 1977 Stored at 35 °C vs 3 °C (pooled over time); Pangborn 1977 Stored 6 weeks (15 °C) vs before storage (bitter aftertaste; table and discussion disagree on significance)]

What is not known — what this comparison alone cannot separate

• The nature of the values differs by study: experiment 2 of Pangborn et al. gives ratios to a control set as 1, pooled over temperatures and addition levels; experiment 3 gives 0–10 scores pooled over pH, gas and serving temperature; Wu et al. use 1–10 scores from a panel of 6–10 (the exact number for each rating not given); and Salek et al. give whole-number medians on 5 points that hide small differences. Values are not compared across studies. [rows: Pangborn 1977 Stored 132 days vs 6 days (median day of the evaluation period); Pangborn 1977 Stored 6 weeks (25 °C) vs before storage (bitterness); Wu 2011 30 °C for 12 weeks vs fresh (kept at 4 °C); Salek 2022 Stored 6 months vs 0 months (all 4 beers; equal medians)]
• All tabled rows are bottled beer; no row compares cans with bottles, and no row varies light exposure (Salek et al. stored the beer away from sunlight and UV). The 30 °C of Wu et al. is a high temperature used to speed ageing, and cannot be taken as the same as beer that aged naturally in shops or homes. A study of the natural change over time in commercial lagers (by King and Duineveld) is used on this page only up to its abstract. [rows: Salek 2022 Stored 6 months vs 0 months (all 4 beers; equal medians); Wu 2011 30 °C for 12 weeks vs fresh (kept at 4 °C)]
• The time row of Pangborn et al. pools temperatures and addition levels, and the text gives no separate test of change over time at each temperature. In the refrigeration study there were rises marked as significant in intermediate months, so change cannot be read as going one way with longer storage. Storage periods differ by study (6 weeks; a final evaluation period centred on day 132; 12 weeks; 6 months), and what happens with longer storage is unknown. [rows: Pangborn 1977 Stored 132 days vs 6 days (median day of the evaluation period); Pangborn 1977 Stored 6 weeks (25 °C) vs before storage (bitterness); Wu 2011 30 °C for 12 weeks vs fresh (kept at 4 °C); Salek 2022 Stored 1 month vs 0 months (original wort extract 11.0%); Salek 2022 Stored 4 months vs 0 months (original wort extract 11.5%)]

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: 3, of which 3 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): 8. Rows on perceived bitterness: 8.
• Evidence rows in the lab's ledger these rows rest on: 0. 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: 3 (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 and J-STAGE for studies combining beer storage, ageing or shelf life with human ratings of bitterness, and added the sources already in the lab's ledger. Studies whose full text could not be reached, studies read only as abstracts and studies whose figure values could not be read are marked as such. Studies varying the age of the hops used are not tabled, because they do not compare storage time after packaging. The search described here is a record, not a claim that nothing was missed.

Read in the encyclopedia

• Beer storage and aging — storing beer after packaging
• Iso-alpha acids — the main bitter compounds of beer
• What Is IBU? Beer Bitterness Units vs. the Taste — the topic hub on IBU
• Do beers with higher IBU taste more bitter? — a comparison of IBU and bitterness

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.