Yeasts

Unicellular fungi of the phylum Ascomycota that reproduce by fission or budding and are capable of fermenting carbohydrates into alcohol and carbon dioxide. Some are responsible for food spoilage, particularly in sweetened, acidic, or low-preservative products, while others are economically vital as the agents of breadmaking, brewing, and winemaking, and in the production of single-cell proteins, B vitamins, and other fermentation products. Beyond Saccharomyces cerevisiae, diverse wild and cultured species shape flavour in sourdoughs, lambic beers, kefir, and traditional ferments. In food safety they are mostly benign, though some cause spoilage and a few are opportunistic pathogens. Their management, through pure cultures, hygiene, and process control, underpins modern fermented-food industries.