is an estimate of how much bitterness a sample of hops can deliver to finished beer. The potential is primarily a function of the alpha-acids content of the hops. Brewers and growers will loosely classify hops based in part on ranges of hops alpha acid content; for instance “aroma” hops have 3%–9% alpha acids by weight, “bittering” hops have 5%–13%, and “super alpha” hops have 11%–18%. Bittering potential is also affected by factors that affect both hop acids dissolution during wort boiling as well as boiling time and temperature. The form of the hops affects how well the hop acids are dispersed into wort, and liquid hop extracts are the most efficient in this regard followed by pelletized hops and then by whole cone hops. Hops added at the beginning of a long boil will have greater potential to impart bitterness while hops added at the end of the boil or to finished beer will have much less potential to increase bitterness. The bitterness in beer and wort is measured instrumentally using two different approaches. A liquid extraction using 2,2,4–trimethylpentane (also known as iso-octane) and subsequent analysis in a spectrophotometer leads to the International Bitterness Unit (IBU); however, there are compounds other than iso-alpha-acids, such as some polyphenols and residual hop acids, that will be extracted by iso- octane thereby yielding an IBU value that is typically higher than the actual iso-alpha-acids content. Individual hop acids can also be measured via high performance liquid chromatography. Brewers use a measure called “hop utilization” to gauge effectiveness of converting insoluble hop alpha-acids into soluble iso-alpha-acids, and this is calculated as the amount of hop iso-alpha-acids in the finished beer relative to the amount of alpha-acids added during the brewing process.

See also hop utilization, international bitterness units (ibus), and iso-alpha acids.