Biterness calculation based on %AA and target AAUs

[Blue-Frog]

My notes are all over the place & I am now quite confused;

If all I know is I want 0.75 g alpha acid in 5 gal of beer,

How do I calculate the number of grams hops needed from the %AA reported on the label?

(Assuming the hops get full boil time)

 

[rhys333]

Use the free online recipe calculator at Brewer Friend. Plug in your fermentables, hop amounts and times. Easy as that and its very accurate.

 

[Blue-Frog]

Thanks for the information.

I was not aware of that resource. Unfortunately, it doesn't seem to deal with AAUs. At least not in a direct user interface way. In the mean time, I have convinced myself that I have figured out my notes... yet my math does not match the advanced calculator in your resource.

I want to grasp the concepts behind the magic in the calculators...

Lots of loose ends to tie up!

 

[Cryovenom]

"An Alpha Acid Unit (AAU), also called Homebrew Bitterness Units (HBU) is a measure of hops used - typically for a 5 gallon batch. It can be calculated simply by multiplying the percent alpha acid of the hops used by the number of ounces of hops. For example 3 ounces of 5% alpha hops would be equivalent to 15 AAUs."

Found that on google. Hopefully it helps.

I'm not sure what you mean by "0.75 g alpha acid in 5 gal of beer". 0.75g is an incredibly small amount of anything. It's 0.0264oz

So if you have 0.0264oz of pure 100% Alpha Acid, then according to google you're looking to have 2.64AAU. The lowest AA hop I've got is some 2.5% AA Hallertau, so it would take a little over 1oz of that in a 5gal batch.

Edit: I see you asked how to figure out grams of hops. Let's use my Hallertau as an example with your numbers.
2.64AAU / 2.5%AA hops = 1.056oz
1.056oz * 28.3495g in an oz = 29.94g

It's annoying because AAUs are defined by the oz, not by the gram so you have to keep converting back and forth

 

[Blue-Frog]

These numbers match what I came up with.
Thanks.