Biological fermentation is a process of biological engineering, which uses the metabolic process of microbial cells to produce various useful products. It consists of three core parts: 1, the selection and breeding of microbial culture with specific products; 2. Appropriate equipment and technology provides the best production conditions for the culture and fully utilises their capabilities; 3. The product produced by fermentation is separated and purified to obtain qualified products, i.e. the culture is the basis, fermentation is the key, separation and purification is the guarantee.