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 Home Brew Forums > What's the % ABV?
10-24-2011, 05:10 PM   #1
Beervana
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 What's the % ABV?

I made a very strong beer with 12.2% ABV. I decided to tame it down so I made another beer with 4.2% ABV and blended the two in a 50/50 blend by volume. So equal parts of each beer. I want to determine the % ABV of the blended result - short of a lab analysis. I know it's not a simple linear dilution (meaning the average of the two) and everything I've come across for dilution assumes diluting with water. Does anyone know how to calculate the resulting ABV of the blend?

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10-24-2011, 05:37 PM   #2
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http://winemaking.jackkeller.net/blending.asp

a couple of calculators I think the easier one is the second one down, basically ABV of each and then put in the quantity of your 12.2% and change the amount of the Fortifier (4%) until you reach the ABV desired. From what I ran with 5 gal of 12%, if you add 2 gal of 4% you'll be at around 9.7%.
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10-24-2011, 08:03 PM   #3
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If the volumes were equal it should be an average of the two.

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10-24-2011, 08:23 PM   #4
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+1, I was thinking the same thing. Why wouldn't it be a straight linear dilution?

5 gallons * 0.122 = 0.61 gallons of ethanol
5 gallons * 0.042 = 0.21 gallons of ethanol

Upon blending you have 0.82 gallons of ethanol in 10 gallons total, or 8.2%. Unless I'm somehow under thinking this.

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10-24-2011, 10:38 PM   #5
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Quote:
 Why wouldn't it be a straight linear dilution?
Because volume isn't conserved but mass is so the first thing to do is convert the ABVs of each beer to ABW's by

ABW = ABV*0.791/SG

where SG is the specific gravity of the beer. Now calculate the weight of each volume of beer by W = Vol*SG*.998203. Multiply by the ABWs to find the weight of alcohol in each. Add the weights of alcohol and divide by the sum of the weights of the 2 beers to find the ABW of the mix. Now convert back to ABV. To do that you need the SG of the mixture so measure it or estimated it by a weighted average of the "points" i.e. 40% 1.030 beer with 60% 1.070 beer will probably have an SG of around 1 + .4*30 + .6*70. Now compute the new ABV from ABV = SG*ABW/0.791
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11-24-2011, 10:23 PM   #6
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I'm trying to calculate a similar thing for a big Belgian I made, wondering how I would know the final ABV with this scenario:

9 gals in fermenter of 1.110

at high krauesen I added 3 gallons of 1.065 sugars

FG = 1.012

I guessed this was around 15%.

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11-24-2011, 10:58 PM   #7
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Same technique - conservation of mass. Find density of each liquid by multiplying SG of each by 0.998203 (the density of water). Find the mass of each liquid. Convert the SG's to °P and calculate the mass of extract in each from the °P (mass_extract = mass_liquid*°P/100). Calculate the mass of the water in each by subtracting the extract mass from the total mass of each. Sum the masses of the water and of the extract. Divide the sum of the masses of the extracts by the total mass of water plus extract and multiply by 100. This is the effective OG in °P for the mix. Apply the expected RDF or ADF to calculate the apparent or true extract. Subtract from the OG and multiply by the proper Balling factor for the OG. This is the ABW. Divide by 0.791 and multiply by the specific gravity of the finished beer (as obtained from the AE estimate if you estimating before the beer finishes). There will be some error from the water lost to evaporation during the fermentation.

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11-25-2011, 07:57 AM   #8
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Whew, more complex than expected, thanks, I'll have to print that out and try to figure it. Any water loss was fairly minimal because I got 11 gallons out of the 12, which is typical with my fermenter.

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11-25-2011, 01:39 PM   #9
ajdelange
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If you go and plug it into a spreadsheet you will probably find it's not as bad as it looks and once it's in the spreadsheet then you don't have to worry about the complexity any more.

Also, if you know that you are losing a gallon to evaporation you can account for that by subtracting 3.78 kg from the total water mass.

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11-25-2011, 01:50 PM   #10
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Quote:
 Originally Posted by ajdelange Same technique - conservation of mass. Find density of each liquid by multiplying SG of each by 0.998203 (the density of water). Find the mass of each liquid. Convert the SG's to °P and calculate the mass of extract in each from the °P (mass_extract = mass_liquid*°P/100). Calculate the mass of the water in each by subtracting the extract mass from the total mass of each. Sum the masses of the water and of the extract. Divide the sum of the masses of the extracts by the total mass of water plus extract and multiply by 100. This is the effective OG in °P for the mix. Apply the expected RDF or ADF to calculate the apparent or true extract. Subtract from the OG and multiply by the proper Balling factor for the OG. This is the ABW. Divide by 0.791 and multiply by the specific gravity of the finished beer (as obtained from the AE estimate if you estimating before the beer finishes). There will be some error from the water lost to evaporation during the fermentation.
I can not imagine a scenario where this info would be that important to me.
Good luck though.
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