Adhumulone, one of five identified alpha acid analogues in hop resin, the others being cohumulone, humulone, prehumulone, and posthumulone. Collectively, these alpha acid analogues serve as the precursors to iso-alpha acids, the predominant contributors of bitterness in beer. Adhumulone levels in hops are typically constant at 15% of the total alpha acid content across all varieties, whereas cohumulone and humulone levels vary (20%–50%) depending on variety. Pre- and posthumulone are minor constituents. Only slight differences in molecular structures differentiate all analogues of the alpha acids. In the case of adhumulone, the side group of the molecule is 2-methylbutyryl. Oxidation of hops leads to cleavage of this side group and the production of 2-methylbutryic acid, which has a distinctive, pungent odor similar to Roquefort cheese. This is why oxidized hops are often described as “cheesy.”
