From where did people get the yeast for their bread??
Baking – How was the usage of yeast for bread discovered
bakingbreadhistoryyeast
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Best Answer
The first yeast was "just there" - in the environment, everywhere. People discovered very early on that leaving the dough (or just a flour-water slurry) out would lead to it getting "sour" and "bubbly", thus leavening the bread: What we today call sourdough is in fact a mixture of yeasts and bacteria (lactobacillae).
Early sources are the Bible (-> the explicit demand for of "unleavened" or "unsoured" bread during Passover suggesting that otherwise was the norm) and sources from Ancient Egypt.
The "modern" yeast that was explicitly added was mentioned by Pliny the Elder in his Naturalis historia as a foam skimmed from beer:
Sources from the 18th century describe how the yeast from the brewing process (Saccharomyces cerevisiae) was used for baking, leading to the "specialized strains" of bakers' yeast cultivated separately when the brewers switched to bottom-fermenting yeast (S. pastorianus) in the 19th century, which preferred cooler temperatures and was not as easy to harvest as the top-fermenting types.
The use of separately cultivated yeast allowed to bake "milder" breads than the sourdough types with their typical acidic undertones but is restricted to certain flour types.