A new study by Justin Fay and Joseph Benavides reveals that vineyard (grape wine) yeast and sake (rice wine) yeast come from two separate wild populations. Previous hypotheses on the origins of Saccharomyces cerevisiae assumed that the species originated from a single domestication event of a wild yeast strain. Furthermore, it was thought that wild populations of S. cerevisiae were due to the release of fermenting, baking, or research strains back into the wild.
Fay and Benavides analysis, however, indicates that wild strains of S. cerevisiae harbor more genetic diversity than any of the domesticated strains. Also, the sake strains and vineyard strains cluster into separate clades. This leads the researchers to propose a model whereby S. cerevisiae underwent at least two domestication events (one for sake and one for wine making) from a much more diverse natural population. Strains used for making whiskey and ale and baking bread were not included in the analysis as previous research has shown them to be quite similar to those used for wine making.
The authors estimate that the sake and vineyard strains diverged about 11,900 years ago, and the domestication events occurred some time after that divergence. This is consistent with the earliest known evidence of wine making, ~9,000 years ago (the strains had to diverge prior to the domestication event).
Fay JC, Benavides JA (2005) Evidence for Domesticated and Wild Populations of Saccharomyces cerevisiae. PLoS Genet 1(1): e5