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General Category => General Homebrew Discussion => Topic started by: chrisinestes on April 12, 2010, 10:20:04 pm

Title: Need help calculating ABV after adding distilled alcohol to beer
Post by: chrisinestes on April 12, 2010, 10:20:04 pm
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?
Title: Re: Need help calculating ABV after adding distilled alcohol to beer
Post by: a10t2 on April 12, 2010, 10:35:20 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.
Title: Re: Need help calculating ABV after adding distilled alcohol to beer
Post by: dbeechum on April 12, 2010, 11:30:17 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%