Alpha acid

Alpha acids (α acids) are a class of chemical compounds primarily of importance to the production of beer. They are found in the resin glands of the flowers of the hop plant and are the source of hop bitterness.

Alpha acids may be isomerized to form iso-alpha acids by the application of heat in solution. Iso-alpha acids (iso-α-acids) are typically produced in beer from the addition of hops to the boiling wort.

The degree of isomerization and the amount of bitter flavor produced by the addition of hops is highly dependent on the length of time the hops are boiled. Longer boil times will result in isomerization of more alpha acids and thus increased bitterness.

Common alpha acids include humulone, adhumulone, cohumulone, posthumulone, and prehumulone. The most common iso-α-acids are cis- and trans-isohumulone.