I know what I'm reading in the winemaking-FAQ:
(Start SG - Finish SG) / 0.0074 = % alc
That's easy enough. It's not consistent with what I think I'm understanding from Pambianchi who calculates down to a finishing SG of
1.00 regardless of the actual value which often is < 1.00.Which is correct?
The former seems more reasonable to me.
There are a number of formulae for calculating potential alcohol, and they are ALL estimates. The tabular values were obtained empirically using distilled water and sugar in a laboratory. (There are simply too many variables to do otherwise, and actual results will vary accordingly.) Most, if not all, formula, are attempts to express "mathematically" what has been measured empirically.
Here are a few formulae, and summary of their derivation and factors:
There are all sort of formula, some are very complex and others overly simple. I can give you the formulae I use which is derived from Duncan and Acton's "Progressive Winemaking" and checked against the basic PA tables that are out there (most of which will lead you astray). It is
% Alcohol = (Go - Gf) / F
Where Go is original gravity and Gf is final gravity and gravity is defined as
G = (SG-1)*1000.
And F is a value that takes into account the non fermentable solids in the must and is defined
F = 7.75 - 3*(Go - 7) / 800
Email me directly if you would like a write up on this.
Ray
I generally use the latter formula as it correlates with the potential alcohol scale on my hydrometer.
Great link. Much obliged.
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