Spectrophotometric measure of iso-octane-extractable material absorbing at 275 nm, conventionally used as a proxy for beer bitterness.
苦味単位（BU/IBU）はperceived bitterness intensity or iso-α-acid concentration in dry-hopped beerを確実には反映しない支持あり
範囲: Dry-hopped and highly hopped beers; pilot-scale and commercial surveys in three independent studies
注記: Three independent lines: an IBU rise driven by humulinones while iso-α-acids fall (Parkin 2017), BU values tracking humulinones rather than perceived bitterness quality (Rutnik 2022), and hop phenolics reaching concentrations comparable to the resins the test is meant to capture (Calvert 2026). Existing clm-beer-bu-nonlinear covers the nonlinearity of the BU-to-intensity relation; this claim is the separate proposition that the proxy also fails compositionally.
IBU rose as a result of dry hopping while total iso-α-acid concentration fell in a majority of the surveyed commercial beers, so the measured IBU change did not track the compound class it is conventionally read as measuring.
限界: Abstract-level extraction; the abstract does not give the size of the IBU rise or the iso-α-acid fall, nor how many of the 15 beers showed the decrease.
The paper states in its beer-bitterness discussion that 'The BU method is most frequently used when the bitterness of beer is in question. However, BU values do not always correlate with the actual perceived bitterness', and that 'The BUs were correlated with the levels of humulinones'. In the data, measured BU rose then fell with HSI (Aurora 22, 29, 39, 35, 34 BU and Styrian Wolf 21, 25, 45, 42, 35 BU across HSI 0.3-0.7) while panel-rated bitterness quality was highest at HSI 0.3 (Celeia 4.9 +/- 0.21, Aurora 4.9 +/- 0.21, Styrian Wolf 5.0 +/- 0.16 on a 1-5 scale) and declined thereafter. For Celeia, iso-α-acids fell from 0.64 +/- 0.05 mg/L at HSI 0.3 to below the limit of detection at HSI 0.6 and 0.7 while BU stayed in the 21-28 range.
限界: Bitterness quality and BU are different scales and were not correlated statistically against each other in the text read; the divergence is inferred from the two tables read side by side, which the paper does not itself state as a correlation result. Ten assessors and one brewing trial per cell. The iso-α-acid concentrations reported for these beers are very low in absolute terms, consistent with dry-hop-only bittering, so they should not be compared directly with kettle-hopped beers.
Highly dry-hopped styles contained the highest concentrations of hop phenolics, up to 159 mg/L, that were comparable to or exceeded those of humulinones and iso-α-acids in the same beers. The authors state that while humulinones are known contributors to the soft bitterness of hazy styles, the role of hop phenolics remains poorly understood, and conclude that hop phenolics may play a more significant role in bitterness and mouthfeel of modern dry hopped beers than previously thought.
限界: Abstract-level extraction and a compositional study: no sensory panel result is reported in the abstract, so the bitterness and mouthfeel implication is the authors' suggestion rather than a measured perceptual outcome. Beer count is not stated in the abstract.
データを表示
concept-bitterness-units —does_not_reliably_track→ "perceived bitterness intensity or iso-α-acid concentration in dry-hopped beer"claim: clm-ibu-not-tracking-perceived-bitterness / type: sensory / 更新: 2026-08-30
範囲: Pilot-scale dry hopping of an unhopped ale at 0-16 g/L for 0-72 h, plus a survey of 15 commercial Pacific Northwest beers sampled pre- and post-dry-hop
注記: The two halves move in opposite directions: the conventional IBU proxy goes up while the compound class it is meant to proxy goes down. This is the central falsification material for treating IBU as an iso-α-acid readout.
A trained sensory panel quantified increases in bitterness from dry hopping an unhopped ale at 0-16 g/L for 0-72 h, alongside IBU and hop acid and polyphenol measurement. The increase in beer bitterness (IBU) resulting from dry hopping was attributed to humulinone extraction and, in some cases, polyphenol extraction. A parallel survey of 15 commercial beers sampled pre- and post-dry-hop noted a decrease in total iso-α-acid concentrations in a majority of the samples tested, indicating that the dry-hopping process may remove iso-α-acids from beer.
限界: Abstract-level extraction. Panel size, IBU magnitudes and iso-α-acid concentrations are not given in the abstract, and the paired sensory result for the commercial survey is not stated. The abstract still names iso-α-acids the main contributor to beer bitterness overall, so this is a qualification of the IBU proxy rather than a displacement of iso-α-acids.
データを表示
process-dry-hopping —increases→ concept-bitterness-unitsclaim: clm-dry-hopping-raises-ibu-lowers-iaa / type: processing / 更新: 2026-08-30