Water soluble fraction of autolysed yeasts. During autolysis, yeast enzymes hydrolyse cytoplasmic proteins and carbohydrates. Insoluble cell wall material (cellulose) is removed, e.g. by centrifugation, to leave a clear extract of water soluble cellular material that is rich in amino acids and other nutrients. Yeast extracts are used as flavourings, as a source of nutrients for microbial fermentation, and as a source of B group vitamins for fortification of foods.