specific question about adjusting hops when using different %AA

I was looking to brew a beer that used tattnang at 3.2% with

1 oz at 60 min
0.5 oz at 45 min
0.5oz 30 min
90 min boil

I got some saaz i would like to use but it is at 5.8%. My guestion is should i keep the ratios the same and aim for the same IBU or should i drop the 60 min down and keep the late additions close to 0.50 oz. In general how does one adjust for differences in %AA when there is multiple additions?

For "late" additions, you don't need to adjust them. However, you don't have any late additions, only bittering so you'll need to adjust all of your additions. It's a pretty easy conversion, but I hate math so I just use software to do it for me.

If you do it "by hand", this blurb from John Palmer explains it best:
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.

cool i got beersmith ill try and see if i can fig it out in there thanks!

The way I adjust bitterness is to divide one AA% by the other to get the new weight. The recipe calls for 3.2% and you have 5.8% and 3.2/5.8=.55 so that means you need .55 ounces instead of 1 ounce for the 60 minute addition. That's the calculation my LHBS told me and it seems to work, although I'm not too picky when it comes to weighing hops.

ekjohns said:

I was looking to brew a beer that used tattnang at 3.2% with

1 oz at 60 min
0.5 oz at 45 min
0.5oz 30 min
90 min boil

I got some saaz i would like to use but it is at 5.8%. My guestion is should i keep the ratios the same and aim for the same IBU or should i drop the 60 min down and keep the late additions close to 0.50 oz. In general how does one adjust for differences in %AA when there is multiple additions?

Click to expand...

It's really just simple math...

For the 1 oz: 3.2 / 5.8 = .55 oz to equal 1 oz of the 3.2

For the .5 oz: .55 / 2 = .275 (you can use .25 or .3 depending on the sensitivity of your scale)

so what times are considered late additions where the %AA no longer matters?

15 mins from end of boil to 0 mins. Adding hops late only extracts its aroma or flavor, but no bitterness.

That's why it's not all that important in mentioning the AA% in the recipe except for bittering.

homebrewer_99 said:

15 mins from end of boil to 0 mins. Adding hops late only extracts its aroma or flavor, but no bitterness.

That's why it's not all that important in mentioning the AA% in the recipe except for bittering.

Click to expand...

I'd even say a 20 minute addition wouldn't really matter much, since the difference in the IBUs extracted would be negligible.