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Old 03-21-2011, 04:05 AM   #1
ckwatson
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I have some questions about figuring out my alcohol content. When I use my specific gravity and do the math (OG-FGx105) gives me a ABV of 3.57 when I use the alcohol scale from my hygrometer it gives me a reading of 4.5 (6.5%-2%) Is this normal?

 
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Old 03-21-2011, 04:07 AM   #2
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The formula used by most is:

OG-FG x 131...

 
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Old 03-21-2011, 04:08 AM   #3
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(OG-FG)x 131. thats what I was always told?
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Old 03-21-2011, 04:12 AM   #4
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The alcohol potential scale on your hyDrometer is probably less precise than the specific gravity scale, so using a formula to calculate ABV from specific gravity is likely the best way to get good results.

The formula you're using is for approximating alcohol by weight (ABW). The ones posted above are correct for alcohol by volume (ABV).
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Old 03-21-2011, 04:31 AM   #5
ckwatson
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Thanks for the heads up on the ABW, when I use 131 I get very close to the 4.5% from the alcohol potential scale.

 
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Old 03-21-2011, 09:57 AM   #6
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The potential alcohol scale on your hydrometer is intended for winemakers. It doesn't work for beer with it's proteins and unfermentables.
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Old 03-27-2011, 05:27 PM   #7
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I think that OG-FGx105 was stated in Papazian's book... I tried it and soon found it to be wrong. I wound up playing with the numbers and comparing them to Beersmith's figures until I settled on 130, but I'm sure 131 is right there...
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Old 03-27-2011, 09:05 PM   #8
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Both are correct.

x 105 will give you the percentage of alcohol by weight in the beer.

x 131 will give you the percentage of alcohol by volume in the beer.

 
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Old 03-27-2011, 10:08 PM   #9
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I've been using the formula in the Cooper's directions. OG-FG/7.46 + .5= approximate %ABV.
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Old 03-28-2011, 12:29 AM   #10
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Quote:
Originally Posted by unionrdr View Post
I've been using the formula in the Cooper's directions. OG-FG/7.46 + .5= approximate %ABV.
Time to change. Check out a few web sites for calculators and you will see which is correct.

 
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