Yeasts are unicellular members of the fungi kingdom and include those commonly found in baking and brewer's yeast, which are of the species saccharomyces cerevisiae. A member of the fungi phylum ascomycota, S. cerevisiae is also known as a "true yeast" because it reproduces by budding. Yeasts are eukaryotic organisms that are unable to obtain their nutritional needs by photosynthesis and require a reduced form of carbon as a food source.
Yeasts in the ascomycota phylum, such as brewer's yeast, or S. cerevisiae, have proven to be useful in research as a model eukaryotic organism. As a unicellular organism, yeast cells develop into colonies quickly, often doubling in population size in between 75 minutes to 2 hours. Because S. cerevisiae reproduces by meiosis, which creates separate pairs of chromosomes, it is a popular candidate for genetic research.
Yeasts play an important role in industry, particularly in the areas of food and beer. Brewer's yeast gets its name from its use as a fermentation agent in the beer industry and cerevisiae means "of beer" in Latin. The carbon dioxide produced during S. cerevisiae's fermentation process is also an often-used leavening agent in making bread and other baked goods. Yeasts are considered one of the earliest domesticated organisms known to man and can be found naturally in the skins of certain ripened fruits.