Industrial fermentation is as a rule a controlled process using pure cultures of production strains in a carefully balanced nutrient medium. It is rarely possible to use selective media to prevent the growth of contaminating microorganism so that the production strain can grow freely. These processes usually employ complex nutrient mixtures, suitable for the growth of a large spectrum of contaminating organisms. In most cases natural nutrients are added, containing usually a high level of microbial contamination. For this reason it is necessary to use sterilization in an effort to eliminate all microorganisms present and thus enable the pro- freely.