View Full Version : attenuation?

03-31-2006, 04:58 PM
Hi, I just got a job as a brewer's apprentice, and after reading about apparent attenuation and actual attenuation, was wondering the difference. We just made a stout, and the O.G. was 14.6 P. The gravity we measured after we crashed the beer was 3.2 P. We multiplied that by .554, and the result (as I understand it) is the ABV. Is this right? If not, can somebody explain how we should be figuring out the actual alcohol content of our beers? And what the difference between apparent and actual is. My boss tried to explain it to me, but I'm not sure he really knows.

Fred Scheer
04-03-2006, 04:06 PM

To give you an example how the Government wants us to
calculate alcohol in TN:

(OG - FG)*.129*.785 = alcohol by weight.


Specific gravity (SG) is a measure of the density of a liquid, with respect to water.

The original gravity (OG) of a wort is the specific gravity reading prior to fermentation.

The final gravity (FG) is the specific gravity of the beer after fermentation.

apparent attenuation = ( ( OG in points - FG in points ) / OG in points ) x 100

Apparent attenuation is different (higher) than the actual attenuation, because the alcohol produced during fermentation is lighter than water, and throws the reading off.

I hope this helps

Fred Scheer :p