Alpha acid

Alpha acids are bittering compounds found in hops that are extracted when hops are boiled with wort. The alpha acid "rating" on hops describes how much of the weight of the hop is made up of alpha acids. Hops with a higher alpha acid content will contribute more bitterness than a low alpha hop when using the same amount of hop.

For example, this list shows a number of hop varieties with the highest percentages of Alpha Acids typically found in each variety (percentages are based on total weight).
* BULLION 11%
* CASCADE 8%
* CENTENNIAL 11.5%
* CHINOOK 14%
* CLUSTER 8.5%
* CRYSTAL 5%
* EAST KENT GOLDINGS 7%
* EROICA 14%
* FUGGLES 5.5%
* GALENA 14%
* HALLERTAUER HERSBRUCKER 5%
* HALLERTAUER MITTELFRUEH 5%
* LIBERTY 6%
* MT. HOOD 8%
* NORTHDOWN 9.95%
* NORTHERN BREWER 10%
* NUGGET 14%
* PERLE 9.5%
* SAAZ 5%
* STYRIAN GOLDINGS 7%
* SUMMIT 19.5%
* TARGET 12.5%
* TETTNANG 6%
* WILLAMETTE 7%