Yeast

Yeast (Saccharomyces cerevisiae) is a species of fungus in the Saccharomycetaceae family that has been instrumental in human food production for millennia.  It occurs naturally on the skin of some fruits, such as grapes and plums.  It is believed that it was first used in winemaking, and from there the organism was isolated for other uses. It is now widely used for fermentation in many products (such as winemaking, brewing, and kombucha tea), as well as a leavening agent in baking.