Stopping fermentation 281I follow you, I'm in Amarillo now so can't speak to what I use as the minimum level but should be home tomorrow. I have bypbutt...
Yeast can undergo different changes, which can affect fermentation, in response to their environment. They can undergo physiological changes and they can undergo mutational or genoimic changes.
Researchers consider any change that undergoes the yeast population after about 20 generations to be a physiiological change. That is the yeast are still the same strain, they just have turned on different genes and re doing differnet things. As a winemaker you cannot really do anythign about that...but these fchanges are minor and not a big problem.
Changes that undergo a yeast population after about 200 generations are considered to be mutational, that is the yeasts DNA has changes and they have become a different strain. These changes can have significant effects on the fermentation or they may be benign.
Now two things, first wine yeast are pretty much optimized to work in wine, so there is no real change to adapt to. So they do not need to change so much. (although they still do change, but that is a differnt issue called genetic drift). Second, yeast manufactures produce yeast from stocks that are created froma progenitor cell. So they are in theory identical from batch to batch. So if you jsut use fresh yeast, you will be using the same yeast every time. This issue is only really a concern for people that culture their own yeast, or those that seed their vines with yeast (from pomace) and let their wine undergo spontaneous fermentaion.
