Calculating ABV with added booze?

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sivdrinks

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Not sure how to do it. Added 8oz of 80 proof Jim Beam Black to the secondary of an 8.4ABV Imperial Stout, 5 gallons. Any ideas?
 
A quick search turned up this formula:

(Beer Volume(oz) * Beer ABV %) + (Liquor Volume(oz) * Liquor ABV %) / (Beer Volume + Liquor Volume)

If I'm doing this right in your case it would be

(640 * .084) + (8 * .40) / (640 + 8) = 0.0879.. so about 8.8%

Hope that helps. :mug: Now this may be a stupid question, but what would be wrong with taking another gravity reading after adding it and simply recalculating the ABV? I figure that would work unless the extra alcohol somehow messes with the reading.
 
Ya lost me on the math there. The beer is already bottled, took over three months to carb! Guess I should have taken another reading before bottling.
 
(640 * .084) + (8 * .40) / (640 + 8) = 0.0879.. so about 8.8%

That was for your specifications. The only reason is I'm doing the same recipe right now and I've come to 8.8 as well. How did you get 10.17?
 
Now this may be a stupid question, but what would be wrong with taking another gravity reading after adding it and simply recalculating the ABV? I figure that would work unless the extra alcohol somehow messes with the reading.

That gravity reading wouldn't do you any good because you're comparing it to the OG reading which was before the additional alcohol was added.
 
29thfloor said:
That gravity reading wouldn't do you any good because you're comparing it to the OG reading which was before the additional alcohol was added.

Wouldn't the bourbons FG lower the beers assuming it's under the 1.028 of my Stout?
 
Yes, bourbon will lower the FG reading, but that doesn't help you with calculating ABV.

The reason the difference between OG & FG can be used to calculate ABV is because it gives you a measure of the amount of sugar converted to alcohol. If you add to or dilute your mixture, you're now measuring the effect of converted sugar and the dilution...so, unless you correct for the dilution, your math will be off.

Imagine adding another 5 gallons to your batch. Will your gravity drop? Yes. Does this mean you boosted your ABV? Of course not, you've reduced your ABV.

ABV is simply (Volume of Alcohol) / (Total Volume). So the original formula posted is aimed at getting the volume of alcohol of each component. Volume of beer x %ABV of beer = volume alcohol. Volume of bourbon x %ABV of bourbon = volume alcohol. Add together the volume alcohol from beer and bourbon to get your total volume of alcohol, then divide by your total volume.

To be the most accurate, you should covert to weight and correct for temp, but this gets you close enough.
 
The reason the difference between OG & FG can be used to calculate ABV is because it gives you a measure of the amount of sugar converted to alcohol. If you add to or dilute your mixture, you're now measuring the effect of converted sugar and the dilution...so, unless you correct for the dilution, your math will be off.

+1 That makes a lot more sense now. I wasn't even thinking about dilution.

Thanks!
 
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