Alpha Acid Calculations

[resQman4]

I am a new brewer and have done one extract brew which turned out great. I decided to step into steeping grains for my second beer. This is my question. The recipe I am using calls for Kent Goldings 5%AA, 60 min 1.2 oz and Kent Goldings 5% AA 5 min .5 oz. My LHBS only had Kent Goldings in 5.5% AA. I did the math (I think) and it looks like this: 1.2 X 5=6AAU's and .5 X 5=2.5 AAU's for a total of 1.7 oz. Since that is with 5% and I could only Get 5.5% i recalculated (again I think) by dividing my AAU's by 5.5 which gave me 1.09oz for 60 min and .45 for 5 min. This also gave me a grand total of 1.54 oz. Is this right? And do these small differences make a big difference in the IBU's?

 

[Shaneoco1981]

No. In fact, most scales won't even read less then 0.05 oz increments. The amount of IBU difference will be less then 1, so you won't even taste the difference.

 

[resQman4]

Awesome. Thanks a ton

 

[oakbarn]

You really work with HBU. IBUs are somewhat different. But generally you did it right.

1.2 oz * 5 AAU = 6 HBU

X * 5.5 AAU = 6 HBU

X= 6/5.5

X = 1.1 oz

Because your AAU are very close there is little difference. The AAU for a 5 minute are not very important as that is more for flavor and aroma.

Generally I correct for AAU in a recipe if the hops are in for 15 minutes or more. If less than 15, I use the amount stated.

You can also use different hops for bittering (60 minutes). Then if you have some at 13 AAU, you would use only 6/13 or .5 oz.

 

[oakbarn]

HBU = Home Brew Units

 

[resQman4]

Thanks for the help. Still new to me. But man how fun and the rewards, well you know. Can't wait to get off shift and get it on.