What formula is correct for calculating alc %? - Home Brew Forums

 Home Brew Forums > What formula is correct for calculating alc %?

06-04-2008, 04:11 AM   #1
Kiwi_Jonno
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Feb 2008
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For Example:

OG = 1036
FG = 1011

OK so the Coopers Book says this one:

(OG-FG) / 7.46 (plus 0.5% for priming)

So... (1036-1011)= 25
25/7.46 = 3.35% (or 3.85% after priming)

Others use this one:

(OG-FG) x131
So... (.036-.011)=0.025
0.025x131 = 3.27%

If the OG was 1055 and FG was 1010, the 1st method 6.03% (6.53% priming) the 2nd would be 5.90%. So quite a bit different.

Iv heard some Homebrew Books say to add 0.3% for priming, Coopers is 0.5%. What is a more accurate number? The bottle size shouldn't make a difference?

06-04-2008, 04:21 AM   #2
Got Trub?
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Uh... I never calculate the ABV. I have a rough idea based on the OG but I don't waste any time figuring it out.

GT

06-04-2008, 07:30 AM   #3
Kiwi_Jonno
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Quote:
 Originally Posted by Got Trub? Uh... I never calculate the ABV. I have a rough idea based on the OG but I don't waste any time figuring it out. GT
Well that was helpful! Anyone know how much % priming beer adds to the total%?

06-04-2008, 12:41 PM   #4
Eves
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I wont say that the Coopers calculation is wrong. But I wonder if their calculation of adding .5% is due to their special carbonation drops. Priming with priming sugar might be different.

06-04-2008, 01:03 PM   #5
Revvy
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I've always used (OG-FG) x131...and never concerned myself with any change from the addition of priming sugar...methinks it would be negligable.
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06-04-2008, 01:27 PM   #6
ohiobrewtus

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Quote:
 Originally Posted by Kiwi_Jonno (OG-FG) x131 So... (.036-.011)=0.025 0.025x131 = 3.27%
This is the formula that I use.
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Quote:
 Originally Posted by the_bird Well, if you *love* it.... again, note that my A.S.S. has five pounds.

06-04-2008, 02:26 PM   #7
Eves
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Quote:
 Originally Posted by ohiobrewtus This is the formula that I use.
But do you account for priming sugar in your final ABV? I mean the Coopers calculation (minus the priming addition) results in nearly the same value as the OG-FG * 131. So the question remains...what about the priming? When you're dealing with ABV I would think you'd want to account for any ABV added by priming. Especially if that addition is a half a percent.

Lets say a pre-primed beer had an ABV of 5%. If priming were to add 0.5% ABV that would be an increase of ABV of 10%. Seems significant to want to account for it.

06-04-2008, 02:32 PM   #8
McKBrew

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If the .5% of added alcohol matters that much, just use the Coopers calculation, or pick a standard and stick with it. ABV is not exact. You can go to several different online ABV calculators and enter the same numbers and you will get varying results.
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06-05-2008, 01:25 AM   #9
dirtbag
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Quote:
 Originally Posted by Eves But do you account for priming sugar in your final ABV? I mean the Coopers calculation (minus the priming addition) results in nearly the same value as the OG-FG * 131. So the question remains...what about the priming? When you're dealing with ABV I would think you'd want to account for any ABV added by priming. Especially if that addition is a half a percent. Lets say a pre-primed beer had an ABV of 5%. If priming were to add 0.5% ABV that would be an increase of ABV of 10%. Seems significant to want to account for it.
um . . . 5 + .5 = 5.5, not 10.

Either way, priming (with sugar) adds such a menial ammount of alcahol to your brew that you really shouldn't even take it into account . . . it's more like .05%. it's the equivalent of adding .0004 to your FG then doing the (0G-FG)*131 formula. Basicly, it's a very, very menial ammount, so don't worry about it.

06-05-2008, 02:07 AM   #10
Got Trub?
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Quote:
 Originally Posted by Kiwi_Jonno Well that was helpful! Anyone know how much % priming beer adds to the total%?
My point was it doesn't really matter. Unlike commercial brewers we don't get taxed based on our production of alcohol so unless you want bragging rights for some triple IPA you brewed who cares?

GT