Beer Forum

Ok, trying to work out the apparent attenuation on a strain that has no rap sheet. This is how I worked it out, let me know if I'm completely off the mark.

Sample recipe
10#'s Pale malt 27 GU's per pound per gallon at 75% effeciency
2 #'s Cane Sugar 46 GU's per pound per gallon at 100% effeciency
=
270 GU's from the Pale, 92 from the sugar for a total of 383 GU's.

382/5gal = 76.4GU's = 1.076

Lets say the beer finished at 1.010. The simple sugar is 100% fermentable... with it in the equation thats about 86% Apparent Attenuation.

My logic is to remove the simple sugar from the equation... and just measure the rest, to find the real apparent attenuation for the yeast strain.

92/5gal = 18.4GU's = 1.018 GU's from Simple sugar.

1.076 -0.018 = 1.058

Then I would use that for the apparent attenuation calculation... 48 GU's/58GU's for an apparent attenuation of 82%.

Is it safe to assume that the apparent attenuation I got would be 82% in this scenario? My only issue with this, is that the Specific Gravity of the Alcohol produced by the simple sugar is less than 1.000 bringing the FG down artificially even when it factored out. Meaning... w/o the sugar, maybe the recipe would give 1.058 and finish at 1.012 instead.

Am I making any sense, or am I just being a little too anal? Thanks for any responses, or if anyone knows the correct/proper way to calculate this, I'd be greatful!

apresskibrewer wrote:Ok, trying to work out the apparent attenuation on a strain that has no rap sheet. This is how I worked it out, let me know if I'm completely off the mark.

Sample recipe
10#'s Pale malt 27 GU's per pound per gallon at 75% effeciency
2 #'s Cane Sugar 46 GU's per pound per gallon at 100% effeciency
=
270 GU's from the Pale, 92 from the sugar for a total of 383 GU's.

382/5gal = 76.4GU's = 1.076

Lets say the beer finished at 1.010. The simple sugar is 100% fermentable... with it in the equation thats about 86% Apparent Attenuation.

My logic is to remove the simple sugar from the equation... and just measure the rest, to find the real apparent attenuation for the yeast strain.

92/5gal = 18.4GU's = 1.018 GU's from Simple sugar.

1.076 -0.018 = 1.058

Then I would use that for the apparent attenuation calculation... 48 GU's/58GU's for an apparent attenuation of 82%.

Is it safe to assume that the apparent attenuation I got would be 82% in this scenario? My only issue with this, is that the Specific Gravity of the Alcohol produced by the simple sugar is less than 1.000 bringing the FG down artificially even when it factored out. Meaning... w/o the sugar, maybe the recipe would give 1.058 and finish at 1.012 instead.

Am I making any sense, or am I just being a little too anal? Thanks for any responses, or if anyone knows the correct/proper way to calculate this, I'd be greatful!

I think your math is basically correct, but your apparent attentuation would be 86% for the first scenario and 82% for the second scenario. Remember, the SG of alcohols produced from malt sugar is less than 1.000 also. The residual sugars are not in a solution of pure water. They are in solution with water and ethanol. That is why this is called apparent attenuation and not "real attenuation" or just "attenuation." It is the easier calculation.

Yeah, I think I was being a little too fixated, but since I've been brewing belgians w/ quite a bit of simple sugar, I wanted to try and figure out what the AA% would be if it weren't present.... It's the ommegang yeast strain, and I think its definitely around 80-82%, sans any simple sugar. (But, with the sugar, its clocking in right around 85-87%)

bump* Any other thoughts?

Even an estimate of what 1% ABV or ABW of alc. in solution would do to the FG...?