Dumb Question

I've lost the bit of paper that I had it written down on, what is the formula to figure out %ABV?

Reply to
Spanky
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I just subtract the FG from the OG, and multiply by 133.

Reply to
David M. Taylor

You can get pretty darn close with (OG-FG)*.131

------------>Denny

Reply to
Denny Conn

According to Coopers, (OG-FG/7.46) + 0.2

Where the 0.2 is allowance for the sugar in secondary fermentation.

So for SG = 1.042, FG = 1.006 you get (1042 -1006) = 36

36/7.46 = 4.8 (approx, 4.8322) 4.8 + 0.2 = 5.0% ABV

Cheers

Reply to
David

For homebrew purposes you can say OG-FG*0.130 where OG and FG are whole numbers (ie no decimal point) so if OG is 1040 and FG is 1010 then ABV is

1040-1010*0.130 which gives 3.9%

In reality the 0.130 varies and HMC&E use a figure between 0.125 and 0.135 as follows:

CALCULATION OF ALCOHOLIC STRENGTH

1 If you have no, or minimal, laboratory facilities, you may calculate the alcoholic strength of your beer by multiplying the number of degrees by which the beer has attenuated by a factor. In order to ensure that your calculations are accurate, it is imperative that the OG. is established as soon as possible after collection and before fermentation commences, which will normally be within one hour of completion of filling the fermenting vessel.

2 The present gravity (PG - also known as the specific or final gravity) should be measured once fermentation is completed. For cask conditioned beer this will be after secondary fermentation in the casks.

3 The OG and PG of representative samples should be measured using a suitably calibrated sacharrometer adjusted for the temperature of the sample.

4 When you have taken your readings, the formula for the calculation is:

(OG - PG) x f = a% ABV

where OG is the original gravity of the beer;

PG is the present gravity of the beer;

a is the beer's alcoholic strength; and

f is the factor connecting the change in gravity to alcoholic strength.

The value of "f " is not constant because the yield of alcohol is not constant for all fermentations. In lower strength beers, more of the sugars available for fermentation are consumed in yeast reproduction than in producing alcohol.

5 The table below produced by the Laboratory of the Government Chemist shows the changing value "f" depending on the alcoholic strength of the beer.

(OG - PG) % ABV Factor Up to 6.9 Up to 0.8 0.125

7.0 - 10.4 0.8 - 1.3 0.126 10.5 - 17.2 1.3 - 2.1 0.127 17.3 - 26.1 2.2 - 3.3 0.128 26.2 - 36.0 3.3 - 4.6 0.129 36.1 - 46.5 4.6 - 6.0 0.130 46.6 - 57.1 6.0 - 7.5 0.131 57.2 - 67.9 7.5 - 9.0 0.132 68.0 - 78.8 9.0 - 10.5 0.133 78.9 - 89.7 10.5- 12.0 0.134 89.8 - 100.7 12.0- 13.6 0.135

The table indicates that for the majority of popular UK beers, the factor for calculating the estimated strength would lie in the range 0.128 and

0.129. For strong beers (exceeding 6% ABV), the factor would be in the range of 0.131 - 0.133. Whilst it is important that the correct value for "f" is used, you should be aware that this table is primarily for your guidance. Some brewing methods and materials can affect the factor.
Reply to
Andy Davison

Thanks everyone, it seems that multiplying the difference by 130 gives a close enough measure.

Reply to
Spanky

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