How much hops do I use?

[rjolin01]

In the past I would just purchase and extract kit and brew. I have recently decided to give all grain a try and look up recipes and collect the ingredients. One source I use is "Brew Your Own" magazine. The thing is that they list their hops in a way I am not sure I understand.

Here is an example:

6 AAU Tenttnang hops (1.5oz of 4% alpha acid)

My guess is that with hops the alpha acid can fluctuate a bit so they want the brewer to adjust amount accordingly? So if I purchase this hop and it's at 4% I would use 1.5 oz but if I get a batch that's say 3% I would need to use 2 oz to get the 6AAU (3%x2oz=6?)

Is this a correct understanding? If not please break it down to layman terms for me!

 

[filthyastronaut]

I'd recommend a beer recipe utility such as Beersmith or Brewer's Friend. They can help with calculations like that! I don't usually rely on manual calculations for that sort of thing, because there isn't much reason to, really. There are a number of convenient options that pretty much do it for you if you give them the right information.

 

[rjolin01]

Did little looking around myself and found this by John Palmer:

"Calculating Alpha Acid Units
AAUs are a good way to state hop additions in your recipes. By specifying the amount of alpha acid for each addition, rather than e.g. 2 oz of Cascade, you don't have to worry about year to year variation in the hop. An AAU is equal to the % AA multiplied by the weight in ounces.
For Example:
1.5 oz of Cascade at 5% alpha acid is 7.5 AAUs. If next year the alpha acid percentage in Cascade is 7.5%, you would only need 1 oz rather than 1.5 oz to arrive at the same bitterness contribution."

So I was correct with my guess!

In neither BeerSmith 2 nor Brewer's Friend do I see anything referring to AAUs!

 

[stz]

I do weight x AA of what is required / AA of what you've got. So if you need 42g at 4% you'd need 56g at 3%. It would work with oz as well.