I have an all grain recipe from Austen Homebrew Supply (AHS) for a clone of Stone Imperial Russian Stout. The expected OG is 1.096 and the expected FG is 1.020, and it calls for using White Labs English Ale Yeast (WLP002).
Based on my calculations, I would need an attenuation of around 79% to hit that FG value. White Labs spec for this yeast says that the typical attenuation is 63-70%, so it seems to be a nearly impossible task without doing something else.
I've been reading the "Yeast" book by Chris White, and it suggests that high OG beers (over 1.090) probably need to be aerated with pure oxygen. It also suggests adding a second yeast that is more tolerant of high alcohol and SG levels during the last third of the fermentation.
I don't have the ability to do pure oxygen, but I'm thinking about the option to add a California Ale Yeast (WLP001) after the WLP002 has gotten the SG down to 1.030 or so.
Anyone have any experience and/or thoughts on this?