Yeast is a single-celled fungus that is scientifically classified under kingdom fungi. Even though single-celled, yeast forms colonies and performs important functions within the food industry by fermenting sugars into ethanol and carbon dioxide. Some of the most widely used yeast strains belong to the species Saccharomyces cerevisiae, commonly known as baker's yeast or brewer's yeast... https://www.zupyak.com/p/4423546/t/yeast-ingredients-the-foundation-for-flavorful-fermentation