I base my calculations on of ABV from gravity on those on the HMRC website, as does the microbrewer I know. Basically because that's what they prescribe and would expect commercial brewers to use. It takes into account the starting gravity. I'll dig it out......
http://customs.hmrc.gov.uk/channels...CE_CL_000232&propertyType=document#P835_96462
"12.2 How can I measure alcoholic strength?
You may use any method you wish to measure the strength of beer as long as it produces results that agree with those that would be achieved using the reference method described in section 29.
If you do not have your own facilities for determining ABV by analysis and you do not add priming sugar, you may use the method (based upon the degrees of attenuation in the beer) which is reproduced at section 30.
If you do add primings to your beers you may use the method which is reproduced at section 31."
(OG â PG) x f = a% ABV
(f in my case is usually 1.29, 1.3 or 1.31, OG-PG 26.2 to 57.1) see table 30.3 on link as it doesn't cut and paste well)
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. The table at 30.3, produced by the Laboratory of the Government Chemist, shows the changing value of âfâ depending on the alcoholic strength of the beer.
(OG - PG)
http://customs.hmrc.gov.uk/channels...CE_CL_000232&propertyType=document#P835_96462
"12.2 How can I measure alcoholic strength?
You may use any method you wish to measure the strength of beer as long as it produces results that agree with those that would be achieved using the reference method described in section 29.
If you do not have your own facilities for determining ABV by analysis and you do not add priming sugar, you may use the method (based upon the degrees of attenuation in the beer) which is reproduced at section 30.
If you do add primings to your beers you may use the method which is reproduced at section 31."
(OG â PG) x f = a% ABV
(f in my case is usually 1.29, 1.3 or 1.31, OG-PG 26.2 to 57.1) see table 30.3 on link as it doesn't cut and paste well)
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. The table at 30.3, produced by the Laboratory of the Government Chemist, shows the changing value of âfâ depending on the alcoholic strength of the beer.
(OG - PG)
