Wild yeast

“Wild” yeast means not dosed from a foil packet. In a Sourdough starter, yeasts live alongside Lactic acid bacteria in a flour-and-water habitat. They produce much of the gas that raises bread. Flour — Wheat flour — is a major source of the microbes a starter captures ¹.

They are not a San Francisco monopoly. 1971 bakery sampling found maltose-negative yeasts (then Saccharomyces exiguus / Torulopsis holmii), not bakers’ yeast, doing the leavening in those sour French doughs ². That ecology is famous, not exclusive. See San Francisco sourdough.

Wine yeast on grape must is a different habitat: more sugar, more alcohol, usually Saccharomyces cerevisiae when inoculated. Do not copy sourdough microbiology onto Wine. Both are Fermentation.