I may be compressing a lot of biology, but I think all fermentation was from ambient yeast until Pasteur figured it out. Then the development of yeast strains suited to particular purposes began. Before that, bakers kept "starter" batter, brewers "pitched" a sample of the last batch, and vintners reused the fermentation vats. And all crossed their fingers that fermentation would proceed faster than spoilage.
Old beverage brewers probably said the same thing we do: "Don't clean it, you'll ruin it!"