« on: September 21, 2015, 11:00:54 AM »
Actually, there is quite a bit of research showing that alcohol exposure does increase alcohol tolerance in yeast. In particular, yeast tend to alter the fatty acid makeup of their membranes in response to increasing concentrations of ethanol, and this in turn enhances their tolerance to alcohol.You want the yeast to be as healthy as possible and the lower the gravity (to a point) the better in that regard. There is no benefit to increasing the gravity and it might even be detrimental.I don't know if I agree with that. If you're starting with healthy yeast from a fresh starter, then my understanding is that you can build up their tolerance to gravity and alcohol in successive generations. That certainly matches my experience, at least. For really big beers I have had great results by pitching from a yeast cake from a batch that was in the 1.060's, which was previously stepped up from a normal-gravity starter or a session beer.
AFAIK, there is no such thing as building up "tolerance". You simply want more healthy cells, and a lower gravity will make sure they're healthy.
As we all know, what happens in a lab doesn't necessarily translate to what happens beer. And you can't apply what happens with one yeast strain universally, either. But it works for me, so I'll stick with it.