Author Topic: Need help calculating ABV after adding distilled alcohol to beer  (Read 617 times)

Offline chrisinestes

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Let's say I have 16 oz of 7% ABV home brew. I add 1 oz of 40% distilled spirits to it... What formula is used to figure the new ABV?
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Offline a10t2

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Re: Need help calculating ABV after adding distilled alcohol to beer
« Reply #1 on: April 12, 2010, 03:35:20 PM »
Since percentages scale linearly, you can just add them proportionally:

((16*7)+(1*40))/(16 + 1) = 8.94% ABV

Edit: It works for any other linear relationship too: specific gravity, IBU, etc.

Edit 2: I really shouldn't try to do things in my head (I divided by 8 instead of 17). Thanks, Drew.
« Last Edit: April 12, 2010, 05:08:11 PM by a10t2 »
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Offline dbeechum

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Re: Need help calculating ABV after adding distilled alcohol to beer
« Reply #2 on: April 12, 2010, 04:30:17 PM »
That seems off to me.. Thinking about it this way:

16 oz of 7% abv = 1.12 oz of ethanol in the pint
1 oz of 40% abv = 0.4 oz of ethanol

So you now have 1.52 oz of ethanol in 17oz of fluid (assuming perfect mixing etc)

1.52 / 17 = 0.089 = 8.9%
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