IS THE RESIN OF HOPS WHICH ARE THE BITTER COMPONENT OF HOP FLAVOR. IT IS MEASURED AS A PERCENTAGE BY WEIGHT.
These come from the soft resin of the hop flower. They are made of humulone, ad-humulone and co-humulone.
A resin contained in the hop plant that is responsible for the bitterness in beer. When purchasing hops, the alpha acid content of the hops will be given as a percentage and printed on the package cover.