formula calculate hop quantity by alpha acid for recipe

[flipfloptan]

Is there a formula to calculate different quantity of hops to add to a recipe if the hops you can get have different AA%. I am not always in a place to input it into a software program.

I am looking at an American Wheat recipe on HBT that calls for .5 oz saaz @ 5.8% 45 min, .25 saaz 25 min and .25 saaz at 0 minutes.

I can only get Saaz at 4.4% AA%. This is for a 2.5 gallon recipe.

Thanks for the help.

 

[Nateo]

http://www.rooftopbrew.net/ibu.php

The calculations are a lot more complex than you could do off the cuff. Well, more than I could anyway.

 

[JLem]

It's really just simple algebra. AA% times quantity should stay constant, so if you use lower AA% hops you need proportionally more

In your case: 0.5oz*5.8AA= 2.9
so if you have 4.4% hops : 2.9/4.4AA=0.66 oz

Note that this is for IBU estimation only - not for aroma or flavor

 

[david_42]

Right, you don't need to change the flavor/aroma adds. Yes, there will be a slight impact on the final IBUs, but in 90% of recipes, the bittering add is all that needs adjustment.