BREWniversity: The Science Behind Hops

Brian P. over at craftbeeracademy.com has started a very interesting and VERY scientific article series on The Science Behind Hops.  Hit the links and be prepared for some SCIENCE IN YOUR FACE!

Part 1: Alpha & Beta Acids

-Cheat Sheet-

• "Alpha acids are generally the bitterness you taste in a beer, and they dissolve into solution immediately. They still take some time to release their bitterness, which is why timing of their addition to the boil is vital. The alpha acids isomerize in the boil to form isomerized alpha acids.
• Beta acids take longer to break down and show up best in lagered or aged beers. Noble hops have the closest 1:1 ratio of alpha to beta hops, where most other hops have about a 2:1 ratio.
• IBUs, or International Bitterness Units, are a direct measure of the iso-alpha acids in a beer. Basically, 1 IBU is equal to 1 milligram of iso-alpha acid per liter of beer."

Part 2: Essential Oils

-Cheat Sheet-

• "Hops main source of flavor and aroma are their oils. More specifically, it is the essential oils that provide the key non-bitter tastes and aromas that hops have. During the boil these volatile compounds evaporate, which is why aroma his are added as close to the end of the boil as possible. 
• Along with the idea of aroma hops being very late additions to the boil comes dry hopping. This is done primarily for aroma, as there is no boil for the essential oils to evaporate. Dry hopping is primarily done to add aroma and is completed by adding hops to the fermentation vessel directly."