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. These would include temperature, relative humidity, and gases that surround the food.