What's my ABV? [hint, it's not ABV% = (OG - FG) x 131.25]

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Larry Sayre, Developer of 'Mash Made Easy'
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Since the old standby formula ABV% = (OG - FG) x 131.25 is woefully inaccurate, what formula(s) offer a better indicator of ABV?

On 'Brewers Friend', they offer an alternative ABV formula as follows:

ABV% = (76.08 * (OG-FG) / (1.775-OG)) * (FG / 0.794)

How good is this formula? It offers quite different values than the old standby...

Are there better formulas?
 
Yes, the Balling Formula in which ABW is estimated as g(OG)*(OE - TE). This can be wickered around to ABW = f(OG)*(OE - AE) which gets you an answer without having to measure TE (which isn't that hard). g(OG) and f(OG) are factors that depend on OG. f= 0.4167 for typical 12 ° beers. f(OG) = n.39661 + 0.0017091*OG + 1.0788E-5*OG*OG. Both OG and FG are in °P in these formulas.

Note that the results produced are w/w.To convert to ABV multiply by the specific gravity of the beer and divide by the specific gravity of pure ethanol (0.79066).
 
ajdelange said:
Yes, the Balling Formula in which ABW is estimated as g(OG)*(OE - TE). This can be wickered around to ABW = f(OG)*(OE - AE) which gets you an answer without having to measure TE (which isn't that hard). g(OG) and f(OG) are factors that depend on OG. f= 0.4167 for typical 12 ° beers. f(OG) = n.39661 + 0.0017091*OG + 1.0788E-5*OG*OG. Both OG and FG are in °P in these formulas.

Note that the results produced are w/w.To convert to ABV multiply by the specific gravity of the beer and divide by the specific gravity of pure ethanol (0.7924).
Click to expand...

Thanks AJ! Could you show an example step by step (using SG readings if possible) so I can see how this works?
 
ajdelange said:
Yes, the Balling Formula in which ABW is estimated as g(OG)*(OE - TE). This can be wickered around to ABW = f(OG)*(OE - AE) which gets you an answer without having to measure TE (which isn't that hard). g(OG) and f(OG) are factors that depend on OG. f= 0.4167 for typical 12 ° beers. f(OG) = n.39661 + 0.0017091*OG + 1.0788E-5*OG*OG. Both OG and FG are in °P in these formulas.

Note that the results produced are w/w.To convert to ABV multiply by the specific gravity of the beer and divide by the specific gravity of pure ethanol (0.7924).
Click to expand...

That's way too much like math.....
 
Ja sure. Beer's original gravity is 1.04644. That's exactly 12 °P. A 75% ADF would give SG = 1.000988 for an AE = 3 °P. OE = 12 implies f = 0.4187 so ABW = 0.4187*(12 - 3) = 3.7863 %. The SG of the beer is 1.000988 and that of ethanol 0.79066 so ABV = 1.000988*3.7863/0.79066 = 4.79%
 
f(OG) = 0.39661 + 0.0017091*OG + 1.0788E-5*OG*OG, is a function of the original gravity. I noticed I had it typed as f(OG) = n.39661 +... You certainly can't be faulted for being confused by that! Or perhaps the notation 1.0788E-5 has thrown you. That means 0.0000107885


In the case of a 12 ° beer f(12) = 0.39661 + 0.0017091*12 + 1.0788E-5*12*12 = 0.418673
 

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