Yeast colonies survived for millennia inside ancient Israeli beer jars
Researchers examining drinking vessels from sites in Israel, some around 5,000 years old, found living yeast colonies still inside them. It was the first direct biological proof that early cultures brewed with yeast, a single-celled fungus that is probably among the earliest organisms humans ever domesticated.
Egyptian ruins had already yielded grinding stones, baking chambers and drawings of bakeries and breweries about 4,000 years old. The English word traces to an Indo-European root meaning to boil, foam or bubble. Anton van Leeuwenhoek saw yeast under a microscope in 1680 but did not recognise it as alive. In 1857 Louis Pasteur proved that living yeast, not a chemical catalyst, drives alcoholic fermentation, and noticed that pumping oxygen in boosted growth while halting fermentation.
Commercial yeast followed. Dutch sellers offered baker's yeast from 1780, solid blocks became possible in 1825, and the filter press improved their manufacture in 1867. Americans relied on wild airborne yeasts until commercial yeast went on sale at the 1876 Centennial Exposition in Philadelphia. Refrigeration freed brewers from the old season; in Montreal, John Molson could brew only from September to May.
Yeasts are not one lineage but a way of living, found in two separate fungal phyla. At least 1,500 species are recognised, around 1 percent of described fungi. Most cells are 3 to 4 micrometres across and multiply by budding, pinching off a smaller daughter, though fission yeast splits into equal halves. Under starvation, diploid cells can form spores and reproduce sexually. Some strains release killer toxins against rivals, which can trouble winemakers. Temperature ranges vary widely, from one species that grows at below freezing to another that prefers 45 degrees.
Baker's yeast, Saccharomyces cerevisiae, likely first came from grape skins and is now among the best-studied cells in biology. Wild yeasts live in flower nectar, where some raise the temperature of stinking hellebore blooms, possibly helping spread scent to pollinators. Others live in the deep sea, in mammal guts, and even between human toes.
Source: Yeast
