Technical Yeast Inquiry
As a disclaimer, I know that there are a handful of past yeast questions on these forums. I have used the search feature and spent a while last night reading through some threads, but I still can't seem to find my information of desire.
What I am wondering about is how well commercial yeast thrives after incorporated into a dough or pre-ferment. On this site, I have read about people claiming that once a poolish or biga has doubled and is no longer growing, it has peaked and should be used at that point. The average time span being around 6-12 hours from my readings. I have read quite a bit of Peter Reinhart's books, Crust and Crumb and BBA in particular. He talks about making your pre-ferment and after it doubles, punching it down and refrigerating it overnight, or up to 72 hours. So, what happens after 72 hours? Or in the case of some of the posts I've read here, after 12 hours? Does the yeast die and start producing off-flavors?
I know that with a natural starter, it can be kept almost indefinitely by feeding it. I guess something I don't understand is why this can't be done with commercial yeast. Does commercial eventually die even if being fed, while natural doesn't?
All of this leads me to wonder why true pate fermentee, or "old dough" is possible. If on day 1 you make a final dough and reserve a piece for the next day, then obviously a portion of day 1 is incorporated into day 2. If you take a piece of day 2 and do the same thing for day 3, then day 3's dough would have elements of not only day 2's dough in it, but day 1's as well. What happens on day 200, when there are still minute quantities of day 1, 2, 3, 4, 5, 6 etc. doughs still being recycled day-after-day? Would this not imply that the commercial yeast is constantly being refreshed and rejuvinated over long periods of time? If so then I wonder why you can't just make a biga or poolish, put it in the fridge, and feed it just like a sourdough or levain over an extended period of time?
This post is the by-product of an immense amount of strong, black coffee and culinary curiosity. If any part of it too "all over the place" just ask me to try to reiterate and I will do so in a less caffeinated state of being.