Understanding attenuation percentage

[JesperP]

Hi everyone

I have noticed that in this forum the attenuation is often being related to the hydrometer measurements in the following fashion:
Att%=(OG-FG)/(OG-1)

but is this a little off due to the alcohol in the finished beer?

I'm just wondering what the yeast manufacturers mean when they write ATT% on the yeast spec sheets.

 

[beerluvva]

Hi

That equation is right...but not sure what you mean by "off a little due to the alcohol"...the alcohol is what produces the FG?

I think the yeast mfr. specified attenuations are statistical performance given a set of initial conditions for the yeast strain.

http://www.whitelabs.com/beer/trial_fermentations.html

In other words, your mileage may vary

 

[beerluvva]

Occurred to me after I posted that you may have been referring to "apparent attenuation", see this from Palmer :

http://www.howtobrew.com/section1/chapter6-1.html

 

[JesperP]

Thanks so what is specified by mfr. is the apparent attenutation and not the "real".