The cells can be multiplied by continuous culture techniques, making use of a fermenter, from which samples can be continuously drawn off, providing a non-stop supply of the product. The fresh medium is added continuously. This ensures that the cells are active and maintained in their log phase of growth. Since the cells can multiply under conducive conditions, a large amount of biomass is obtained and hence the protein. In this bioreactor, nutrients are replaced as soon as they are utilized and products are removed as soon as they are produced.