Hop Adjustment Due to Alpha Acid Difference

I am about to brew the "All Amarillo IPA" from a recipe in the Extract Brewing section here on HB Talk, but I have a question about hop AA%. Should I be adjusting my hop additions if the AA% of my hops is different from what is called for in the recipe? I assume that I should, but I just want to make sure. The recipe calls for Amarillo 8%AA and the Amarillo hops that I bought are 9.3%AA.

So, if I were to convert the following hop schedule...

1.5 oz Amarillo 8%AA for 60 Min
1 oz Amarillo 8%AA for for 15 Min
1 oz Amarillo 8%AA for for 5 Min
.5 oz Amarillo 8%AA for at flameout

It becomes...

1.3 oz Amarillo 9.3%AA for 60 Min
.85 oz Amarillo 9.3%AA for for 15 Min
.85oz Amarillo 9.3%AA for for 5 Min
.42 oz Amarillo 9.3%AA for at flameout

Will these small changes matter much or should I just go with the original recipe?

Thanks in advance for your help!

Jesse

Your calculations are correct. For the recipe you could go either way. It's just a recipe.

According to Ray Daniels in Designing Great Beers, you should only use the IBU formula for bittering addtions (more than 15 minutes of the boil), not for flavoring or aroma.

He gives the formula as:

IBU = (Wgrams x U% x A% x 1000) / (Vliters x Cgravity)

where

Wgrams is the weight of hops in grams.
A% is Alpha Acid level of a hop, as a decimal (e.g., 7% = 0.07).
U% is percent utilization, as a decimal.
Vliters is the final volume of wort in liters (what goes into your fermenter, prior to top-off).
Cgravity is a correction for worts that have a gravity above 1.050, but it also includes cases where you boil a concentrated wort that is later diluted in your fermenter (a partial boil). When the gravity is less than 1.050, the correction factor is 1. If over 1.050, then Cgravity = 1 / [(Gboil - 1.050) / 0.2], where Gboil is the specific gravity of the wort in the boil kettle.

U%, the percent utilization, is given by a table with different values for whole and pellet hops. I'm not going to list the whole table from Ray Daniels' book, but for 60 minutes (the only hop addition you have that materially affects IBU, the U% is .24 (24%) for fresh whole hops, and .30 (30%) for fresh pellet hops.

So to properly calculate the IBUs in your case, you need to base it on the post boil volume and OG during the boil, and prior to top off water addition.

If you decide to reduce your hop additions, only reduce the first one. Leave the rest alone, as the alpha acid percentage is not especially important for the late additions.

Personally, I would not bother reducing the first hop addition either. It won't make 5 IBUs of difference in bitterness, and Daniels' says that studies have shown that most people cannot detect differences in bitterness less than 5 IBU.

EDIT - I checked with Beersmith and actually it will make a calculated difference of 7.2 IBU if you don't reduce the 60 minute adddition. 1.3 oz would be the correct reduced amount to equal the original IBU for an 8% AA hop.

There are a lot of factors that affect bitterness and utilization, so I'm still not sure it makes much real world difference whether you cut the amount or not. I still advise you don't cut the late additions at all.

About .5 oz difference? I'd save it and use it later. But you could always use it all and just get a little more hop presence.

If it was me I would leave it. The 15,5 and flameout additions will not add bitterness just flavor/aroma.

Perhaps the hops were 9.3% at the time they were measured, but they will probably have lost some of that since they were measured. With such a small difference, I wouldn't make any adjustment.

-a.

ajf said:

Perhaps the hops were 9.3% at the time they were measured, but they will probably have lost some of that since they were measured. With such a small difference, I wouldn't make any adjustment.

-a.

Click to expand...

I agree- it's not that much of a difference. The difference between 1.5 and 1.3 ounces is rather insignificant and probably not worth the trouble.

And as was stated, you don't decrease the flavor or aroma additions anyway, as .75 ounces of flavor hops will taste different than 1 ounce and those additions are all about the flavor and aroma. Same with dryhopping- don't adjust those additions either!

Thanks for all of the sage advice. Much appreciated. Happy to be a new member of such an awesome community. Happy holidays to all of you!

Jesse