Product structure. Liquids and semi-solid foods will usually have a homogeneous composition,
but many products do not, including composite foods. Moisture and flavours will migrate between
layers, while coatings and surface treatments can either restrict or enhance the spoilage potential.
For example: herbs and spices on the surface of a pâté may grow mould, but a layer of aspic over
the herbs will exclude air and prevent mould growth; the pastry crust covering a meat pie will make
the content anaerobic, but will allow bacterial spores such as Clostridium perfringens - commonly
associated with meat - to germinate and grow; however anaerobic conditions are less likely with a
potato topping. It is important to understand the structure of your products, for example where there
is the potential for anaerobic pockets to form that could provide the right environment for anaerobic
bacteria to grow.