I had some second thoughts about the info I was passing along, and looked more into it. First of all, the absolute limit of dna splitting may be more of an animal thing... human cells can divide only about 52 times because we cannot duplicate a sort of tail end of our dna. Cancer cells can duplicate that, but our normal cells just countdown our 52 copies.
There is a fascinating tutorial on "the wonderful world of yeast" at http://invsee.asu.edu/srinivas/yeast...ldivision.html
... well, I aimed that at the cell division page, but you can start back on the introduction page by clicking upper left. They do mention that SF sourdough yeast is sort of a myth... it is 99% a certain type of bacteria with only a trace of wild yeast. Maybe that would make a good drink though!
Apparently the exponential phase of yeast growth is a budding process , which gives smaller cells than from true sexual reproduction where two come together to make 4. Some yeast divide evenly, but I get lost in tracking down why store bought yeast may be superior to recycling. Anyway there is interesting info there on the later stages of lifecycle, like how yeast can start digesting themselves and giving bad odors.