Yeast Extract is an autolysate of yeast cells used in preparing microbiological culture media in a laboratory setting. Yeast Extract is not intended for use in the diagnosis of disease or other conditions in humans. Yeast Extract is the water-soluble portion of autolyzed yeast. The autolysis is carefully controlled to preserve naturally occurring B-complex vitamins. Yeast Extract is prepared and standardized for bacteriological use and cell cultures and is an excellent stimulator of bacterial growth. Yeast Extract is generally employed in the concentration of 0.3% – 0.5%.

Yeast Extract is typically prepared by growing baker’s yeast, Saccharomyces spp., in a carbohydrate-rich plant medium. The yeast is harvested, washed, and resuspended in water, where it undergoes autolysis, i.e., self-digestion using the yeast’s enzymes. Yeast Extract is the total soluble portion of this autolytic action. The autolytic activity is stopped by a heating step. The resulting Yeast Extract is filtered clear and dried into a powder by spray drying. Yeast Extract has been successful in culture media for bacterial studies in milk and other dairy products. Several media containing Yeast Extract have been recommended for cell culture applications.