How would one calculate the ABV of a beer if distilled spirits were added? For instance, when making a beer recipe that called for adding bourbon as a flavoring agent. If you started with, say, 5 US gallons of beer at 5% ABV and you added 1 quart of "80 proof" spirits, how would one calculate the resulting ABV?
This seems like a simple solution dilution problem. Take
5 gallons = 20 quarts => 20 quarts * 5% ABV = 1 quart alcohol.
Then take your 1 quart of "80 proof" (40% ABV), and we get
1 quart * 0.4 = 0.4 quarts alcohol
So we have a total volume of 21 quarts (beer plus spirits) and a total of 1.4 quarts alcohol, thus
1.4 / 21 = 6.67% ABV
Unless I'm missing something about ABV percentage,
6.67% should be the final answer.
In general, if we have (making sure we are using consistent units)
O - the original volume, in quarts A - the volume of spirits to add, in quarts s - the % ABV of the original volume p - the % ABV of the spirits
Then we can use the general formula below
((O * s) + (A * p)) / (O + A)