In a study that split the same lager taken from the production line into a sample kept at 4°C and a sample held at 30°C for 12 weeks, a bitterness score on a 1-to-10 scale by an expert panel of 6 to 10 people went from 6.6±0.5 to 3.1±0.4. The paper records the ± only as 「統計誤差」 (in translation: "statistical errors") and does not state its type, the number of independent bottles, or a significance test. This is a comparison under high temperature for 12 weeks, and the same magnitude of decline cannot be applied to all ordinary storage periods.
In a trial that stored a different lager in the dark at 14±0.5°C and compared it against the fresh product using triangle tests by smell alone, a difference was detected in the can at 6 months but not in the bottle. At 11 months, a difference was detected in both the can and the bottle. This is a result from untrained assessors choosing by nose alone, not a comparison of taste or bitterness when drunk. Also, the non-detection for the bottle at 6 months is not proof that it was the same as the fresh product.
A study that tracked lager aged in oak barrels for 300 days using spectrophotometry found that the bitterness value (IBU) decreased stepwise and significantly, from 26.90 at 0 days of aging to 17.90 at 300 days. In addition to the oxidation and polymerization of total polyphenols and their adsorption onto the wood, the cyclization of iso-alpha acids during aging into decomposition products with weaker bitterness is explained as a factor. However, this bitterness value is an instrumental spectrophotometric measurement, and the sensory panel in this study evaluated only 6 aroma attributes such as caramel-like and wood-like aromas; it is not a value in which people evaluated the taste of bitterness.
Ming J. Wu; Frank M. Clarke; Peter J. Rogers; Paul Young; Narelle Sales; Patrick J. O’Doherty; Vincent J. Higgins / 2011 / journal article / full text checked
Checked for this overview: Supports the same lager, the 4°C versus 30°C for 12 weeks comparison, the expert panel of 6 to 10 people, the 1-to-10 scale, the 2 bitterness values, and the fact that the type of ±, the number of independent bottles, and a significance test are not stated.
Ana Carolina de Lima; Laura Aceña; Montserrat Mestres; Ricard Boqué / 2023 / journal article / full text checked
Checked for this overview: Supports storage in the dark at 14±0.5°C, the 6- and 11-month triangle-test results by can and bottle, the untrained, smell-only assessors, and the limitation of non-detection.
Shi Yaqi; Yu Junhong; Xing Lei; Hu Shumin; Chen Hualei; Yan Peng; Shao Shuping; Liu Haixin; Tang Yajie; Yang Zhaoxia; Yin Hua / 2026 / journal article / full text checked
Checked for this overview: Used for the figures on the decrease in IBU over time during 300-day oak-barrel aging, and the limitation that this is an instrumental measurement, not a sensory evaluation
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trans-iso-α-acids →is selectively degraded dur…→ beer storage and aging
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Sensory (2)
beer storage and aging shows the sensory response Comparing a sample of the same lager taken from the production line and kept at 4°C with a sample held at 30°C for 12 weeks, bitterness on the expert panel's 1-to-10 scale went from 6.6±0.5 to 3.1±0.4.supported
Scope: Wu et al. 2011; commercial Australian full-strength lager; QDA by an expert panel of 6 to 10 people.
Note: The paper records ± only as statistical errors, so whether it is SD, SEM, or another type is unknown. The number of independent bottles and production replicates is not stated, and no significance test is shown. The 30°C, 12-week accelerated condition is not extrapolated to ordinary storage in general.
For the lager kept at 4°C right after production and the same lager held at 30°C for 12 weeks, the bitterness scores were 6.6±0.5 and 3.1±0.4.
Limitations: The type of ± is not stated. No significance test, number of independent bottles, or number of production replicates is given. A 5-year vintage product with a different recipe is outside this comparison.
Show dataprocess-beer-storage —has_sensory_response→ "Comparing a sample of the same lager taken from the production line and kept at 4°C with a sample held at 30°C for 12 weeks, bitterness on the expert panel's 1-to-10 scale went from 6.6±0.5 to 3.1±0.4."
beer storage and aging shows the sensory response When the same brand naturally stored in the dark at 14±0.5°C was compared against the fresh product using triangle tests by smell alone, it was detected in the can but not the bottle at 6 months, and detected in both the can and the bottle at 11 months.supported
Scope: de Lima et al. 2023; the same commercial lager; untrained assessors; fresh product compared against 6- and 11-month products by container.
Note: This is a forced-choice test by smell alone, not a drinking or bitterness evaluation. The non-detection for the bottle at 6 months is not proof of equivalence. The number of participating trials differed by test.
For fresh versus 6-month product, the can had 14/26 correct answers (p=0.0247, detected) and the bottle had 12/28 correct answers (p=0.1911, not detected). For the 11-month product, the can had 16/30 (p=0.0188) and the bottle had 17/29 (p=0.0045), both detected.
Limitations: This is detection by smell alone and does not measure taste, bitterness, or preference. Non-detection is not proof of equivalence. Overlap among participants and the assignment details for each sample are not clear from the text.
Show dataprocess-beer-storage —has_sensory_response→ "When the same brand naturally stored in the dark at 14±0.5°C was compared against the fresh product using triangle tests by smell alone, it was detected in the can but not the bottle at 6 months, and detected in both the can and the bottle at 11 months."
trans-iso-α-acids is selectively degraded during beer storage and agingsupported
Scope: Beer stored in brown glass bottles
Note: The scope is deliberately limited to brown glass. The same research group reports that this cis/trans selectivity does not hold for oxygen-permeable packaging. See the limits evidence row.
In beer storage in brown glass bottles, the trans-configuration iso-alpha-acid isomer appeared to decrease extremely specifically and strongly, while the corresponding cis-iso-alpha-acid appeared barely affected.
Limitations: Abstract-level extraction. Storage duration, temperature, and the number of beers are not stated in the abstract. This finding depends on packaging conditions. See the corresponding limits row.
The abstract states that, while it had been established that only the trans-form iso-alpha-acids degrade during beer storage and the cis-form does not degrade, the key transformation products generated only from the trans isomer had not previously been known, and this study identifies them.
Limitations: Abstract-level extraction. The wording "exclusively" is the authors' own summary of prior literature, not a measurement broken down by container in this paper itself. Storage conditions and the number of beers are not stated in the abstract.
Limits: In the same paper, beer storage in polyethylene terephthalate bottles, known for oxygen permeability, induced rapid degradation of both isomers regardless of cis/trans configuration. Correspondingly, model oxidation of cis- and trans-isohumulone, independent of configuration, produced both the cis- and trans-configured hydroperoxy-alloisohumulone and the corresponding hydroxy-alloisohumulone.
Limitations: This limits cis/trans selectivity to low-oxygen packaging; it does not refute the selectivity itself. The abstract does not quantify degradation for either packaging, and does not state how the PET and brown-bottle beers were matched.
An independent HPLC kinetics study on the storage of commercial lager was structured around the degradation of trans-iso-alpha-acids (trans-isohumulone, trans-isocohumulone, trans-isoadhumulone), with activation energy calculated for each compound. In dark beer, degradation of trans-isocohumulone showed a higher activation energy than the other 2, whereas in pale beer and non-alcoholic beer, all 3 were comparable.
Limitations: The abstract does not directly show a comparison with the cis isomer. The trans specificity of aging is something the study design operated on as a premise, and is not re-demonstrated against the cis compound in the body of the abstract.
Scope: An experiment at homebrew scale. Dry-hop contact time was varied from 0 to 96 hours, and trans/cis ratio was compared before and after 30 days of storage at room temperature
Note: The authors state that it was 「概ね(generally)」 (in translation: "generally") lower, and it is also noted that the difference between the 1–12 hour conditions and the 72-hour condition was not statistically significant. The trans/cis ratio is a measure used in prior research as an indicator of beer staling.
In beer stored at room temperature for 30 days, the condition dry-hopped for 24 hours or more showed a smaller change in trans/cis ratio and less oxidative degradation of iso-α-acids during storage than the condition dry-hopped for a shorter time. The authors interpret this as suggesting that dry hopping has a protective effect on beer flavor stability.
Limitations: This remains at the level of the expression 「概ね(generally)」 (in translation: "generally"), and it is also noted that the difference between the 1–12 hour conditions and the 72-hour condition was not statistically significant. The authors also point out the possibility that measurement variability, or a protective effect of wort-derived antioxidants in young beer, may be confounding the result.
beer storage and aging reduces The bitterness units (IBU) by spectrophotometry of a lager aged for 300 days in oak barrels significantly decreased (p<0.05 between each pair of time points) from 26.90±0.6 BU at day 0, to 23.10±0.49 at day 60, 21.65±1.20 at day 100, 21.00±0.57 at day 180, and 17.90±0.57 at day 300supported
Scope: Shi et al. 2026; lager from a Chinese brewing company (Tsingtao Brewery) stored in oak barrels; physicochemical property measurements in Table 1; IBU measured by a modified spectrophotometric method (275 nm)
Note: The sensory panel (QDA, 10 experts) evaluated only 6 aroma attributes—caramel-like, wine-like, wood-like, vanilla-like, sweet, and coconut-like—and did not directly evaluate the taste attribute of bitterness. The bitterness value in this claim is instrumentally measured (spectrophotometric) IBU, not a human taste evaluation. Result of a single product under a single barrel condition.
Table 1 shows the physicochemical properties at 0, 60, 100, 180, and 300 days of oak barrel aging: bitterness (Bitterness, BU) declined 26.90±0.6 → 23.10±0.49 → 21.65±1.20 → 21.00±0.57 → 17.90±0.57, with statistically distinct letters (a→c) assigned, p<0.05. The text explains this by the oxidative degradation, polymerization/precipitation, and adsorption onto wood of total polyphenols, and by the cyclization of trans-iso-alpha-acids into products of lower bitterness.
Limitations: This is instrumentally measured IBU, not a sensory-intensity evaluation of bitterness by an expert panel (the QDA sensory panel evaluated only 6 aroma attributes). Result of a single barrel and single product; the barrel's history (new or previously used) and storage temperature could not be confirmed from the text.
Show dataprocess-beer-storage —reduces→ "The bitterness units (IBU) by spectrophotometry of a lager aged for 300 days in oak barrels significantly decreased (p<0.05 between each pair of time points) from 26.90±0.6 BU at day 0, to 23.10±0.49 at day 60, 21.65±1.20 at day 100, 21.00±0.57 at day 180, and 17.90±0.57 at day 300"