This article is from the WineMaking
FAQ, by malak@CAM.ORG (Don Buchan) with numerous contributions
38 How To Measure Alcohol Levels In Your Wine
To calculate Alcohol by Volume: Subtract the last reading from the
initial gravity and divide the result by 0.0074. This gives the
approximate alcohol content in %.
S.G. = 1.070 F.G. = 0.995
1.070 - 0.995 = 0.075
0.075 / 0.0074 = 10.15%
It does not matter what the first or last reading is, both mean little
alone. The difference between the two does!
Usually there is also an alcohol scale marked directly on a hydrometer;
subtract initial potential alcohol reading from final, and the
difference is the approximate alcohol content.
Using the Brix scale, 1 degree Bx = 1 g/100 ml, or 10 g/liter. When you
read a Bx of say 22, divide the 22 by 2 to get 11, and add 1, for a
final alcohol of 12%. It is an extremely good rule of thumb.
Another method is the boiling method:
- take 250 ml of wine
- measure specific weight and temperature
- boil the wine down to 125 ml
- bring up to 250 ml using boiled water
- cool to the same temperature as above
- measure specific weight
- the difference between the two is related to the alcohol level; use
the following table:
s/w volume %
spec. weight is in gram/litre