Calculating ABV with Liquor additions

Tue Dec 13, 2011 11:12 pm

I've made a Chocolate Oatmeal Rum Stout & a Vanilla Bourbon Porter. How the heck do I calculate the ABV after adding amounts of liquor?
BitterPunk
 
Posts: 17
Joined: Wed Jun 09, 2010 6:56 pm
Location: Victorville, CA

Re: Calculating ABV with Liquor additions

Wed Dec 14, 2011 6:31 am

As long as the amounts of alcohol being added are small you can do it by assuming consevation of volume e.g. if you have 5 gal of beer at 5% abv that contains 0.25 gal of alcohol. If you add 1 quart of 80 proof spirits you would be adding 0.4 quart (0.1 gal) of ethanol for a total of 0.35 gal of ethanol in 5.25 gal of fortified beer. ABV = 100*0.35/5.1 = 6.9%. Accurate calculations are much more detailed than this and require that you can convert between SG and Plato, have "proofing tables" or data on the density of ethanol - water solutions etc. At the levels of this example the extra effort buys minimal increase in accuracy - much less than the uncertainty in your knowledge of the ABV of your beer unless you sent it out for analysis.
ajdelange
 
Posts: 1386
Joined: Wed May 27, 2009 9:18 am

Re: Calculating ABV with Liquor additions

Wed Dec 14, 2011 6:50 pm

Great description! Thanks for the help! After reading a few different things, I decided to use this formula:

(X*ABV) + (Y*ABV2) / (X+Y) = New ABV%

X = Qty of beer
ABV = ABV% of beer
Y = Qty of spirits being added
ABV2 = ABV% of spirits

Note: Proof of Liquor/2 = ABV%
BitterPunk
 
Posts: 17
Joined: Wed Jun 09, 2010 6:56 pm
Location: Victorville, CA

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