What Are AAUs & How Do I Calculate Them?

Sometimes with beer recipes you’ll see next to the hops a number followed by AAU.  If you are new with the world of brewing it’s understandable that you might not have a clue what this means.  An example is below:

5 lbs Light DMe

6 AAUs Fuggle (60min)

10 AAUs Kent Goldings (15min)

Safale 04

What the AAU is referring to is the weight and the alpha acid of that particular hop.

How to get the AAU’s you use this formula:

AAU = Weight (oz) * % Alpha Acids (whole number)

Calculating AAUs for a recipe is a way to ensure that your beer will remain at the same level of hoppyness from batch to batch.  It’s a nice calculation to use because, hops acidity changes from year to year.  Also if you had to substitute hops ever this measurement  will allow you to get a more accurate approach on the bitterness of the hop.

Going back to the example,  if we know AAU and we then know alpha acid (4.2% for Fuggle) and we plug those numbers in it looks like this:

6AAU (Fuggle Hops) = oz * 4

We just need to change around the formula to better fill our needs which is to find out how many ounces we need for this particular recipe.  It would look like this:

oz = (AAU/Alpha Acid)  

Again we just put back the numbers into the formula and plug away:

oz = (6/4)

1.5 oz 

To check our math just put it back in the original formula.

AAU = oz * alpha acid

6 = 1.5 * 4

6=6

We would need 1.5 oz of fuggles at 4.2% to get the, “correct” level of bitterness out of the beer.

Conclusion

The reason why using AAUs for your recipe can be helpful is that even if the crops alpha acid changes from year to year, by using AAUs as your measurement rather than just ounces it will allow you to get a more consistent beer when making repeats.  Hope you enjoyed.

Cheers,