is one of four beta acid analogs in hop resin, the others being adlupulone, lupulone, and prelupulone. Colupulone levels vary across hop varieties from roughly 20% to 55% of total beta acids. Lupulone levels also vary, from 30% to 55%. Adlupulone levels vary in a much narrower range, from 10% to 15%. Structurally, beta acid analogues are very similar, but not identical, to their alpha acid counterparts. The slight structural difference, however, prevents beta acids from isomerizing in the kettle. See hop isomerization. There are, therefore, no iso-beta acids in wort or beer. Furthermore, beta acids are virtually insoluble in wort; thus, only trace levels can be found in beer. When beta acids oxidize into hulupones, however, which happens as hops age, they become wort soluble and confer bitterness. As hops oxidize, the bitterness that comes from iso-alpha acids diminishes, but this is somewhat offset by the contribution of bitterness by hulupones. The ratio of alpha to beta acids ultimately determines the extent to which the bitterness will diminish as hops oxidize.

See also adlupulone, lupulone.