Calculating Adjusted Hop Amounts Due To Adjusted Volume Amounts

So I brewed on Monday :rockin:. And I've just recently started taking my numbers seriously (read VERY seriously). That's become part of the fun for me. So here's what happened.

I adjusted my grain mill and slowed my sparge rate down and went from my traditional 70% efficiency to 79% efficiency. That meant that my collected runnings went from an expected gravity of 7.75gal of 1.043 wort to 7.75gal of 1.048 wort. It was only 5 points. Not a huge deal.

But since I'm brewing a clone recipe, I want to get my numbers right in where the recipe calls for (1.043 NOT 1.048). So I thought...I'll just add some water, bring my volume up and have a bit more beer at the end. I calculated that I would need 1gal of water to bring the gravity down to 1.043. But then that got me thinking. If I add water that'll mess with my bitterness and other hop additions. Because whereas I was supposed to start the boil with 7.75 gallons, I would now be at 8.75 gallons.

Since I didn't know the calculations to make adjustments to my hop amounts, I just left it and figured, I'll make adjustments in the next batch. So...can somebody help me out here?

How do I calculate adjustments to my hop amounts based on an increase (or decrease) in my volumes? I know some of you might not sweat it, but I would like to know "how to do it" before I decide "whether or not to do it." Thanks!

From Designing Great Beers (Daniels, 79)

IBU= Weight(oz.) x U% x A% x 7,489 / (Volume(gal.) x C(gravity))

where:
A% = alpha acid level of hop as a decimal (e.g., 7% = 0.07)
U%= percent utilization (@ 60 minutes use 30%, 15 minutes use 15%, and 5 minutes use 6% as a base unless you know your exact utilization)

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Using this formula you can put your desired IBUs in and solve (if you're any good at algebra). For aroma hops, I'd say take your initial amount, divide it by your planned # of gallons, then just add that amount on for however many gallons you add (or something like that).

I'd suggest just entering everything into a calculator and letting that figure it out for you. Beersmith is the obvious choice, but I use a free online one at hopville.com (it's much easier than doing the math, trust me).

Or you can use software like BeerSmith.

So, I'm just wondering if I can use a percentage change. If my calculations say add 1gal to a 7.75gal batch that is a 13% increase in volume. Could I simply add 13% more of each hop addition? That would add 13% more bitterness, aroma, oils, etc.

Also, I use Beer Alchemy as my software of choice. I think it does this, I've just never used that calculator up to this point.

hafmpty said:

So, I'm just wondering if I can use a percentage change. If my calculations say add 1gal to a 7.75gal batch that is a 13% increase in volume. Could I simply add 13% more of each hop addition? That would add 13% more bitterness, aroma, oils, etc.

Also, I use Beer Alchemy as my software of choice. I think it does this, I've just never used that calculator up to this point.

Click to expand...

Yes, a directly proportional increase is what you want.