OK, once you start messing with hops, the big question is "How much do I have ?", particularly if you don't have a calculator, or for you really groovy types, a slide rule available. Well, there are a few acronyms to know, a few calculations to do, and viola, you'll know. Ready?

AA = Alpha Acids. Alpha acids are the percent of the weight of the hop flower that is alpha acid resin; it is the alpha acid resin that contributes significantly to the bitterness of beer. For example, 6% AA means that 6% of the hop flower weight is the weight of alpha acids alone. Hop varieties differ in their AA percentage. Low AA hops are 2 - 4%, medium are 5 - 7%, and high AA hops are 8 - 12%. Percent AA will decrease with age; a hop that is 7% AA may decrease to 5% AA in a few months, particularly if not properly stored.

HBU = Homebrew Bittering Units. HBU = (%AA of hops) X (ounces of hops). For a recipe calling for 15 HBU of Cascade hops, if your hops were 5% AA, you would need three ounces of hops.

IBU = International Bittering Units. Not all of your AA are available when you've boiled your wort because you lose AA to the yeast and proteins in your wort. Weak worts give higher hop utilization rates; in other words, the higher your original gravity (OG), the lower your hop utilization rate. Some sources claim that 30% utilization is the best that you can hope for when push comes to shove. When making a five gallon batch of homebrew, the formula for the calculation of IBU can be crunched down to:

IBU = (HBU) X (% utilization) / 6.7.

There are other formulas available to do this, but they all basically involve unit conversions, and they are all done in a similar fashion as above. Page 268 in "The New Complete Joy of Homebrewing" has a table listing some hop percent utilization rates. If any of you know of any other sources of this info, e-mail us and let us know.

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