Each filament is referred to as a hypha . The mass of hyphae that can quickly spread over a food substrate is called the mycelium . Moulds may reproduce either asexually or sexually, sometimes both within the same species. There are a number of factors that affect the survival and growth of microorganisms in food. Each microorganism has a maximum, optimum, and minimum aw for growth and survival.
Yeasts are able to grow in a more acid environment compared to bacteria.
Moulds can grow over a wide pH range but prefer only slightly acid conditions. Milk has a pH of 6.6 which is ideal for the growth of many microoorganisms. Milk, however, is a fluid product with no barriers to the spreading of microorganisms throughout the product. More information on these antimicrobials can be found in a chapter on dairy microbiology and safety written by Vasavada and Cousin . Where the intrinsic factors are related to the food properties, the extrinsic factors are related to the storage environment.