Attentuation Question

[Sudz]

The recipe I'm looking at shows a OG of 1.077 and a FG of 1.009. If I calculate the attenuation from these numbers I get 88%. Yet the yeast specified is rated at 70%. That suggest to me that there's no way for that yeast to ferment to 1.009 even if everything is perfect.

I assume there's something here I am failing to understand. What am I missing?

 

[flars]

Yeast manufacturers publish an attenuation rate for comparisons of yeast. The published attenuation is from the fermentation of a standard wort. Real attenuation is based upon the available sugars in the recipe being fermented.

You can have two all grain beers with the same OG. One beer mashed at 160°F and the other mashed at 146°F. The beer mashed at 146° will reach a lower gravity than the former because more fermentable sugars were produced.

Hope this makes some sense.

 

[lslbrew]

Is any of the OG made up of corn sugar, honey, or another sugar that ferments 100%. That would make your average attenuation higher than the yeast rating.
If all grain, what is the mash temp? You can increase the fermentability with temp but I would not expect an extract to recipe to estimate 88%.

 

[flars]

Is any of the OG made up of corn sugar, honey, or another sugar that ferments 100%. That would make your average attenuation higher than the yeast rating.
If all grain, what is the mash temp? You can increase the fermentability with temp but I would not expect an extract to recipe to estimate 88%.

All my extract brews have always attenuated to a higher percentage than the published figures for the yeast. No pure sugar used in any of the recipes.

 

[lslbrew]

All my extract brews have always attenuated to a higher percentage than the published figures for the yeast. No pure sugar used in any of the recipes.

Agreed that you can get higher attenuation than the mfg states, but on a 1.077 beer, if it was from extract, I doubt that you can get 88% without some 100% fermenting sugars. An extract malt just has too many unfermentable sugars to get down to 1.009 from 1.077.

 

[Sudz]

Thanks guys. I understand the error of my ways. Was "assuming" the published yeast specs were based on 100% fermentables under ideal conditions. That they are not explains it all.

Cheers...