What are alpha acids, AAUs, HBUs, and IBUs?
Alpha acid resins only contribute to the bitterness of the beer. Occurring naturally in the lupulin gland on the hop cone they are not very soluble in water. The reason that hops must be boiled is because the heat of boiling water creates a condition that allows a chemical reaction, called isomerization, to occur which makes the alpha acid resins soluble in water. AAU stands for Alpha Acid Units and is a measurement of potential bitterness in hops. The percentage of alpha acid in a given sample of hops multiplied by the weight in ounces of that sample. One ounce of hops with an alpha acid content of 1 percent contains 1 AAU, or .01 ounce of alpha acid. HBU stands for Homebrew Bitterness Units and is another method by which home brewers can determine how much hops to use. Homebrew Bitterness Units equals the percent alpha acid of hops multiplied by the quantity in ounces of hops used. If for example a recipe of a given volume of beer calls for, say 2 ounces of 5 percent alpha acid Casca
