Formual to calculate Alchohol Percentage

[kizzo]

hey guys


What is the best formula to calculate alchohol percentage and how does amount of water in fermenter and bottling with carbonation drops affect the alchohol percnetage?

I have read that you simply get yor start gravity and minus from your finish gravity, then times it by 131. Yet my home brewer sais to times it by 135-137????

I dont understand how this can be so varied? Should there not be a standard fomular to follow to calculate?

Also, I dont fill my fermenter to 23L as per directions. I fill it to approximately 21L.....does this affect alchohol percentage?

I am bottling at the moment, so carbonation drops increase alchohol percentage also???




cheers

 

[Ducatiboy stu]

At 21L it will be higher in Alc %. How much I dont know because I dont know what the starting gravity is.

 

[indica86]

[SIZE=12pt]Calculating Alcohol by Volume (Alc/Vol)[/SIZE]
There are many calculators out there that estimate the alcohol content of beer using Specific Gravity (SG) readings. They all pretty much follow the formula:
Alc/Vol % = (OG – FG) x f
Where:
OG = Original Gravity = Specific Gravity of the beer before fermentation
FG = Final Gravity = Specific Gravity of the beer after fermentation
f = a correction factor connecting change in gravity with alcoholic strength
Unfortunately f is not constant and ranges from 125 for weak beers to 135 for strong beers (Briggs, Boulton et al. 2004). Many alcohol calculators will simply use an f value of around 130 and not take into account variations. To make our calculator more accurate than most we have used f values produced by the Laboratory of the Government Chemist in the UK. For taxation purposes the UK government have released a table of f values to be used in alcohol calculations for small breweries. This is shown in Table 1 below:
Table 1. f values for various beer strengths (HM Revenue and Customs (UK) 2008).

(OG – FG)

% ABV

Factor (f)

Up to 0.0069

Up to 0.8

125

0.0070 – 0.0104

0.8 – 1.3

126

0.0105 – 0.0172

1.3 – 2.1

127

0.0173 – 0.0261

2.2 – 3.3

128

0.0262 – 0.0360

3.3 – 4.6

129

0.0361 – 0.0465

4.6 – 6.0

130

0.0466 – 0.0571

6.0 – 7.5

131

0.0572 – 0.0679

7.5 – 9.0

132

0.0680 – 0.0788

9.0 – 10.5

133

0.0789 – 0.0897

10.5 – 12.0

134

0.0898 – 0.1007

12.0 – 13.6

135

http://pint.com.au/calculators/alcohol/

 

[ianh]

Saved me from finding this. In my spreadsheets I use 131 as the factor, but you can use 130 or 131 for most beers. The error in measuring the OG and final SG is greater than the error from the factors.

Plus you also need to take into account the extra sugar added by the carbonation drops when bottling.

 

[Grott]

I've always used the Cooper calculator - (OG - FG) / 7.46 + .5 for the priming sugar.
Cheers