Source: Homebrew Stack Exchange Question/Response
So you’ve decided to brew a stout and want to flavor it with some bourbon. Or maybe you’ve made a gose with extra salt and some lime and you want to dose it with a bit of tequila. Or maybe you want to clone an Innis and Gunn beer but you don’t have a barrel so you’re just going to add some scotch straight to your keg. Or maybe you’ve made a hot pepper tincture in a quart of vodka that you plan to add to your summer pilsner. I think you should do all of them because they all sound delicious!
Hang on though. Once you’ve added the bonus booze, how do you determine the new alcohol by volume (ABV) of your boozy brew? I was faced with this question recently and below is what I learned.
Recalculating Your ABV
What we have here is a solution dilution equation. It’s one I’ll explain using an example. I know you want me to get to the point but humor me here.
For the example, let’s assume you have a base beer that’s five gallons and 5% ABV. You want to add 1 quart of 80 proof (40% ABV) liquor.
The calculation goes like this:
- 5 gallons of beer = 20 quarts
- 20 quarts of beer * 5% ABV = 1 quart of alcohol
- 1 quart of liquor * 40% ABV = 0.4 quarts of alcohol
- Total volume = 21 quarts (20 beer + 1 liquor)
- Total alcohol = 1.4 quarts (1 beer + 0.4 liquor)
- New ABV = 1.4/21 = 6.67%
Now that you’ve been patient, here’s the formula:
New ABV = ((B * o) + (L * a)) / (B + L)
- B – the beer volume, in quarts
- L – the volume of liquor to add, in quarts
- o – the % ABV of the original volume
- a – the % ABV of the liquor addition
Now go make a list of all the boozy beers you want to make!
Now that you’ve read this Homebrew Tip, let me know if you have a question, recommended improvement, or other thoughts in the comments below. As I mention in About Homebrew Notes, these are living documents and your feedback is appreciated!