Attenuation is the % of sugars a yeast will consume during fermentation, and is a general gauge of how much ABV will result from a specific OG solution.

We all know that the attenuation of a specific yeast has a % rating on its data sheet. But how is this number calculated and given an officially accepted value for its data sheet?

Yesterday I attended a private class at a White Labs San Diego. Hoping to get a clear answer on this. Erik Fowler was presenting and did an awsome job, and did his best to answer many of our questions. The answer I got to the my question in this case is that there is a standard wort recipe used to calculate attenuation. But he didn't know exactly what that "control" in the test is.

The question came up when we were presented a couple flights of beers using the same wort and different yeast. He made it clear that the attenuation data shown for this flight was specific to these batches.

I feel it's imprtant to know what this control recipe is so a brewer can accurately predict attenuation for a given recipe. I'm sure the conrol recipe is something simple and a best guess of an average for most styles say a 1.040 OG, with 90% simple sugars (fermentable) and 10% complex (difficult to unfermentable). And then the fermentation conditions are ideal for a given strain.

Since attenuation is effected by so many factors we need to know what it's rating is based on, not just an assumption that it's an average wort.

It's safe to say any brewing yeast out there has 100% attenuation in a low OG mono-saccaride solution.

If anyone knows this control recipe from an authoritative source, please post it here.