Alpha Acid

Alpha Acid. (ael'-fuh ae'-sid)

One of the two soft resins in hops. It consists of three closely related chemical compounds- humulone, co-humulone, and ad-humulone- and forms 2-14 percent of the total weight of hop cones and approximately 45 percent of soft resins. Alpha acids have a low wort solubility, and about 90 percent of beer bitterness is caused by compounds that form during boiling, the most important of which are iso-alpha-acids (iso-humulones), which account for most of the bitterness. The conversion of alpha acids to iso-alpha-acids takes from one half to one and a half hours; however, this may vary because the solubility of alpha acids decreases with increasing wort gravity. During aging, alpha acids oxidize and lose approximately 30 percent of their bittering power after one year and about 40 percent after two years. See also beta acid, soft resins.