Alpha Acid question?

[arborman]

Ok, so to better understand this number, are all numbers given using the same formula? For example, I am doing a Moose Drool tomorrow, and the AA numbers given in the recipe call for 4.75% AA on my bittering hops, but the hops I got are 7.2%AA. I used the adjust bitterness in beersmith so I hit my IBU number, but this got me thinking: Are all these percents given using the same formula? I got my hops at Moorebeer.

What is the default formula being used by beersmith and the places that sell the hops? Am I correct that I should be adjusting my IBU to match what I want, based on my hops having a higher AA then what was called out for in the recipe?

 

[JLem]

The alpha acid % is determined analytically by a lab. You need to adjust your recipe using the actual AA% on the package. For IBUs to a given level...you'll need less hops of a higher AA% or more hops of a lower AA%. The easiest way to figure all this out is to change the AA% of the hops in your software or online recipe calculator.

Please note however that 1) different IBU estimation methods used different algorithms (Tinseth, Rager, etc) - just choose one and stick with it; 2) the AA% only impacts IBUs, not flavor or aroma - a higher AA% hop does not mean it also has higher aroma potential. When using hops for flavor and aroma, keep the ounces/gallon the same. Your IBUs may be impacted, but you can then adjust your bittering addition up or down to hit your target IBUs.

 

[BigEd]

Am I correct that I should be adjusting my IBU to match what I want, based on my hops having a higher AA then what was called out for in the recipe?

Yes. Hops in a beer recipe aren't like sugar and flour in a cake recipe, they change.

Hops are an agricultural product and the AA will vary from season to season, grower to grower. So armed with the information JLem provided you also need to check the number on newly purchased hops and adjust accordingly. Adjustment is also usually required when substituting hops.