Formula for calculation included.
Attenuation
Attenuation is defined as the %sugar converted to alcohol and CO2 by the yeast. Apparent attenuation is computed from the measured specific gravity (converted to extract) of the beer, as follows:
AA = 1 - AE / OE,
AE = Apparent Extract of beer, as measured by a hydrometer
OE = Original Extract of the wort.
However, the specific gravity of the beer is depressed by the lower specific gravity of alcohol (0.8, approximately), so the measured apparent extract is smaller than the real extract (sugars remaining in the finished beer). Real extract, RE, can be measured by dealcoholizing the beer (typically by boiling gently), adding distilled water back to the original volume, and then taking the specific gravity. Or, we can use an approximation (due to Balling):
RE = .1808*OE + .8192*AE,
With this approximation, we can compute an approximation to the real attenuation as
RA = 1 - RE / OE,
RA = 1 - (.1808*OE + .8192*AE) / OE.
Delpo