Calculating ABV with added booze? - Home Brew Forums

 Home Brew Forums > Calculating ABV with added booze?

12-14-2011, 11:49 AM   #1
sivdrinks

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Apr 2011
Lebanon, PA, PA
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Not sure how to do it. Added 8oz of 80 proof Jim Beam Black to the secondary of an 8.4ABV Imperial Stout, 5 gallons. Any ideas?

12-14-2011, 12:52 PM   #2
bomberman
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Oct 2011
Middlebury, VT
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A quick search turned up this formula:

(Beer Volume(oz) * Beer ABV %) + (Liquor Volume(oz) * Liquor ABV %) / (Beer Volume + Liquor Volume)

If I'm doing this right in your case it would be

(640 * .084) + (8 * .40) / (640 + 8) = 0.0879.. so about 8.8%

Hope that helps. Now this may be a stupid question, but what would be wrong with taking another gravity reading after adding it and simply recalculating the ABV? I figure that would work unless the extra alcohol somehow messes with the reading.

Reason: math error!

12-14-2011, 05:38 PM   #3
sivdrinks

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Lebanon, PA, PA
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Ya lost me on the math there. The beer is already bottled, took over three months to carb! Guess I should have taken another reading before bottling.

12-14-2011, 06:09 PM   #4
theveganbrewer
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Sep 2011
Beaverton, OR
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Sounds about right. He just calculated the percentage for the whole batch. Each bottle will be about 8.8%.
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12-14-2011, 06:18 PM   #5
sivdrinks

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K, did it. Came up with 10.17. Thanks!

12-14-2011, 06:19 PM   #6
sivdrinks

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Quote:
 Originally Posted by theveganbrewer Sounds about right. He just calculated the percentage for the whole batch. Each bottle will be about 8.8%.
Now I'm lost again.

12-14-2011, 06:23 PM   #7
theveganbrewer
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(640 * .084) + (8 * .40) / (640 + 8) = 0.0879.. so about 8.8%

That was for your specifications. The only reason is I'm doing the same recipe right now and I've come to 8.8 as well. How did you get 10.17?
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12-14-2011, 06:28 PM   #8
sivdrinks

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My bad, disleksic. You're right, thanks again!

12-14-2011, 06:35 PM   #9
SenorPepe
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Feb 2011
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Very timely thread for me. Thanks, folks.

12-14-2011, 06:55 PM   #10
29thfloor

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Feb 2011
Pt. Pleasant, PA
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Quote:
 Originally Posted by bomberman Now this may be a stupid question, but what would be wrong with taking another gravity reading after adding it and simply recalculating the ABV? I figure that would work unless the extra alcohol somehow messes with the reading.
That gravity reading wouldn't do you any good because you're comparing it to the OG reading which was before the additional alcohol was added.
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