I'm planning to brew a very high gravity stout. I'm expecting an OG between about 1.118 and 1.138 depending on how much my efficiency suffers. I've done this before with decent results, but I think I can provide a better fermentation than I have before.
I'm planning to mash pretty low (140-145F) so that I will have a very fermentable wort, and to minimize residual sugars.
I expect that I will want to use two yeasts; one to achieve the desired flavors (esters) and one to brave the extreme alcohol concentration and eat what it can. I'll probably stick with something like Wyeast 1272 (American Ale II) for the former; the latter I am a bit unsure about.
In the past, I've used champagne yeast, and I can't say I really had problems with it. However, even with a mash focused in the beta-amylase range, I still had a pretty sweet beer -- even after aging for a couple years. I'm wondering if another high-alcohol-tolerance yeast might attenuate a little better.
To this end, I'm considering using another yeast, like the Wyeast 775 Cider Yeast, that claims to attenuate much higher (over 80%). Wyeast even claims in its description of the yeast that it can be used for high gravity beers. In my case in particular, can a yeast really affect attenuation that much?
More subjectively, would you recommend another yeast for high alcohol fermentation?
I'm planning to ferment a bit lower to help keep excessive esters / fusel alcohols out. Something like 66F. Is this appropriate, or will I be hampering fermentation?
Lastly, should I let let the "base yeast" ferment until it has virtually stopped before pitching my high-alcohol-tolerance yeast, or should I pitch as it nears its theoretical tolerance limit? I ask because I'm concerned about the effects that might occur when the yeast hits its limit.
Edit: I'm aiming for a 10 gallon batch.
More Edit: I'm shooting for as much attenuation as possible. If I can get it up near 80, I'll be quite happy. I think I'll make a low gravity Dry Stout as a starter (5-10 gallons at about 1.040).