Yeast extracts are concentrates of the soluble components of yeast cells and traditionally produced by autolysis. It means that the cell hydrolysis is performed without addition of external enzymes. Yeast extracts are mainly used in the fermentation industry as substrates and in the food industry as flavour improvers.
The major raw material for yeast extract is primary grown high protein yeast, which is grown on molasses. In the USA, yeast extracts are also manufactured from debittered brewers yeasts. Autolysis is the most frequently used disruption method in yeast extract production. In this process, yeasts are degraded by own internal enzymes. The autolysis process can be initiated by a controlled temperature or osmotic shock, causing the yeast cell to die off without inactivating its own endogenous enzymes. Controlled pH, temperature, and duration of the autolysis are critical factors for an optimal autolysis process. By addition of salt or enzymes the protein degradation of the yeast cell can be controlled.
For the production of yeast extracts containing five prime nucleotides special strains of primary grown bakers yeast are used as raw materials. Under normal autolysis conditions, the RNA is mainly degraded to three prime nucleotides. However, flavour enhancing properties have only been found in 5 prime nucleotides. By use of spesific enzymes some 3’-AMP is converted to 5’- IMP. Yeast extracts containing 5’- IMP have significantly increased flavour enhancing properties. Dependent on the process, duration of the autolyses can vary from 15 to more than 60 hours. After completion of the autolysis the soluble cell components are separated from the insoluble cell walls and then concentrated by falling film evaporators. A further concentration step, carried out in a partial vacuum, provides the typical product types. Liquid, viscous paste and dried powder forms are main types of yeast extracts. Some manufacturers also use drum driers for special applications.
Cell wall fraction is a byproduct of yeast extract production process. Yeast cell walls are marketed either as liquid or as spray-dried products.