ASBC Methods of Analysis - Beer-23: Beer Bitterness
ASBC Methods of Analysis
Reports of the Subcommittee on Determination of Isohumulones in Beer for 1967 and 1968 indicate that bitterness units (BU), as determined by the two techniques described in Method A, express the bitter flavor of beer satisfactorily, regardless of whether the beer was made with fresh or old hops. The European Brewery Convention has adopted the “E.B.C. Bitterness Units,” determined in a similar way, as a uniform method that best expresses the true bitter flavor value of beer. Method B, which was archived but has now been reinstated, and Method C determine iso-a-acids (IAAs). Method B employs solvent extraction, while Method C uses solid-phase extraction for isolating the IAAs from beer. Method D is an automated version of Method A for measuring BU. While the results of the IAA methods are practically identical to those obtained by the BU method for beer brewed with fresh hops, the IAAs of beer brewed with old or poorly stored hops, and with certain special hop extracts, can be significantly lower than the BU figure.
Hops are traditionally added during the boil to extract alpha acids that provide the bitter flavor in beer. Brewers are more frequently using a technique of dry-hopping beers to improve the flavor and aroma in the beer. Dry hopping is frequently done in the fermenter or cask. This process does not add any bitterness to the beer because they have not been boiled in the kettle and the hop acids have not been isomerized. So in effect the dry hopping does not add to the bitterness of the beer. When analyzing a dry hopped beer the possibility of the ultraviolet-absorbing extraneous substances is greater in the BU methods than in the IAA method. The current IBU method overestimates the bitterness in dry hopped beers. To account for this a calculator has been employed to estimate the IAA portion of the IBU result when analyzing dry-hopped beers.