where does yeast come from.
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The product you’re thinking (down thread a bit) of is called Brewer’s Yeast, and it’s one of the more useful discoveries of human kind. It’s also one of the older ones.
Yeast is a fungus, single cellular, that “eats” sugar and starch and “expels” ethanol and carbon-dioxide. There are hundreds of different strains, think of them like breeds of dogs or cats, each has slightly different properties, but they are all closely related.
Thousands of years ago all yeasts were “wild” yeasts, multiplying in warm, moist, sugar-laden environments, and when the moisture dried up the fungi would also dry themselves out in a shell to protect themselves until the next time it is moist, warm, and sugar-laden. Dried up single-celled fungus is very light and easily picked up by breezes, and that allows the fungus to spread easily.
Eventually humans realized that fruit that had landed on the ground and started to rot actually made alcohol, and since the humans wanted the buzz they gathered fruit and specifically allowed it to rot. Do this enough times and you learn what to do and what not to do to make it turn out good. But the magic of why rotten fruit became alcohol wasn’t perfectly known, but what DID become known is that the foam that forms on top of mash for beer or wine, if introduced to another vat of juice or mash would make the process go faster and be more reliable.
Brewers would dry their foam, making a powder of it, and pour a goodly amount of the powder into their mash, and over time that made a few strains of yeast that are now known as Brewers’ Yeast. Eventually they tried adding the yeast to doughs made of flour and water, and the resultant breads were lighter, fluffier, and tasted better. The strains of yeast were eventually isolated and are now cultured, companies like Fleischmann’s have giant vats of mash that regularly have more starch and water added, with air bubbled up through it to keep the mix from killing off the yeast culture, and they skim material off at the same rate. The material pulled off is FULL of yeast, they then reduce the water content carefully (you can buy “wet block” yeast, it’s harder to work with but more reactive) until it’s the right level, package it up, sell it, and then bakers use the material to make bread and beer and wine and pizza dough and everything else that needs the same type of yeast each and every time.
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