What formula is correct for calculating alc %?

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Kiwi_Jonno

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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?
 
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.
 
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.
 
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.
 
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.
 
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
 
um . . . 5 + .5 = 5.5, not 10.

Actually it is 10. Perhaps I need to be more clear:

10% * 5 = 0.5 <- right?

So 5 + .5 = 5.5 that means that the alcohol level increased from 5 to 5.5. Which is an increase of 10%. Now I know .5% doesn't seem like a big increase but when you consider that some people go out of their way to squeeze out a little more ABV without too much impact on their final product it would be nice to know what the true increase of priming is.

As for the Coopers carb drops I see no reason to believe they're lying about them adding .5% ABV. I just question whether or not the use of priming sugar or other brands of carb tabs also increase the ABV by that much.
 
Actually it is 10. Perhaps I need to be more clear:

10% * 5 = 0.5 <- right?

So 5 + .5 = 5.5 that means that the alcohol level increased from 5 to 5.5. Which is an increase of 10%. Now I know .5% doesn't seem like a big increase but when you consider that some people go out of their way to squeeze out a little more ABV without too much impact on their final product it would be nice to know what the true increase of priming is.

As for the Coopers carb drops I see no reason to believe they're lying about them adding .5% ABV. I just question whether or not the use of priming sugar or other brands of carb tabs also increase the ABV by that much.

Assuming that the Coopers Carb drops carbonate the beer the same amount as priming with sugar, the same alc % should be added surely? The Homebrew Book I read (was a good one) said priming adds 0.3% so perhaps it is more then ya think?

Reading the Coopers formula again... it doesn't state if the priming is using its drops or sugar. It recommends 180g sugar for the 23L or 6gal (us) batch.

And I guess knowing the EXACT % isn't overly important, but I like to know roughly for future batches I guess.
 
A "typical" priming solution containing 4 oz of corn sugar adds ~11 gravity points to your 5 gallon batch. That's a little over 2 points per gallon.

.002 x 131 = 0.26% ABV
 
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

Well, I for one would like to know the approximate strength I'm drinking or serving.
Since taking hydrometer readings is part of my program, doing the quick math to get an estimate is worth it to me and only takes a couple seconds.

I just use the "(OG-FG) x131" method for the approximate strength and leave it at that. I don't worry about priming sugar additions as its minimal in the big picture.
 
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