To cultures that valued bread and beer above other processed foods, yeast carried central importance, both nutritionally and culturally. A common family of sin-gle-celled fungi that reproduce by budding, yeasts include the all important Saccharomyces cerevisiae, which ferments the sugars derived from flour to produce the ethanol and carbon dioxide gas that raises dough. A variant strain, called barm or brewer’s yeast, ferments cereal, hops, and malt to make ale and beer. Another strain, the ellipsoideus, transforms grape juice into sparkling wine. Dried yeasts also supplement other foods with B-complex vitamins, vitamin D2, and protein.