Calculating ABV with a post-fermentation alcoholic additive

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splattsmier

Well-Known Member
Howdy! New to the forums, so I apologize if this has been answered already.

I'm brewing up a Bourbon Barrel Porter and plan to add 375mL of bourbon to racked porter just before bottling. My question is: How would I go about adjusting readings to correctly calculate my final ABV? I haven't tried this before, so any and all advice is welcome.

dwarven_stout

Well-Known Member
First of all, that is a *lot* of Bourbon to add. You can always add it "to taste" in the bottling bucket.

Secondly, all you need to do is determine the final gravity normally before adding the bourbon. Then, multiply the alcohol % of the bourbon by the volume fraction of the bourbon in the bucket (probably something like 40% * .086gal /5 gal, since 325mL = 0.086gal) and add this number to the number you got by comparing initial gravity and final gravity. You'll be adding less than 1% alcohol to the finished product.

Lennie

Well-Known Member
I've seen 1/2 cup used for a popular 5gal recipe, you're talking 1.3 cups. I agree thats a lot of bourbon. I personally don't like that much bourbon flavor in a porter/stout. You might but I'd do a taste test first since you can't remove it once its been added.

And to finish off dwarven's calculation, its an additional 0.7%.

GaryJohn

Well-Known Member
Being someone who is mathematically challenged, this is how I do it. Someone can tell me if I'm wrong.

First, find out how much pure alcohol is in the bourbon. You added 375 ml, and bourbon is 40% abv let's say. So that means you added 150ml of straight alcohol (150ml is 40% of 375ml). Then you have to figure out how many ml's of beer you have. 5 gallons = 18,927.05 ml. So 150ml of pure alcohol into 18,927.05ml of beer is 150/18,927.05=.0079.
So I'd say you upped it by about 0.8%.

That's roughly what the other person calculated, so I think it's right.

OP
S

splattsmier

Well-Known Member
Thanks for the input everyone. As suggested I added in increments, but did end up using the full 375mL.

Final ABV is 7.4%.

OP
S

splattsmier

Well-Known Member
So, after nearly a year I feel I need to say - this beer turned out AMAZING. For the first several months the Bourbon was overpowering, but it has aged with ineffable grace. I plan to brew this again after my Imperial Porter and let it sit for 9 months or so before reaching into the stash. Next time I'm going to use a different whiskey as the MM was definable even after the 1 year. Not bad by any means, but I think I'd prefer something like Knob or Wild Turkey 101. With this new combo I fathom it will hold up to - dare I say - Dragon's Milk, and maybe even KBS (just recently found its way to Texas, YES!).

Still, it's been my most praised brew after ~15 batches.

zachattack

Well-Known Member
Hey I don't think it's too much, the only beer I did with a whiskey/oak addition I used a full pint of rye.