4. Material and Energy Balances

Before a food manufacturing process can be installed and commissioned into a factory, it must be designed and the size and nature of the equipment to be used must be specified. However, before this stage an analysis of the process must be undertaken to determine, inter alia, the quantities of product and raw materials to be handled. This process analysis step consists largely of a material balance and an energy balance. Process analysis itself is preceded by a concept stage at which the broad outline of the food manufacturing process is decided upon. For example, the concept may involve, for a given product and a given rate of production, a series of operations such as mixing, evaporation, pasteurisation, filtration, drying, freezing and packaging with specified values of important quantities at each stage. In other words an answer must be found to the question, How is the product to be manufactured? When the concept has been established the very first step in the process analysis is a material balance. This allows the mass flow rate and composition of the various process streams to be determined. Thus the necessary inputs for a given production rate can be calculated or alternatively the output rate for given raw material feed rates can be determined. It is often the case in food processes that the material balance is relatively trivial, perhaps because relatively few components and few process steps are involved, although in such cases the procedure described in the next section is still extremely useful. Even where the material balance is trivial the energy balance (often reduced to a ‘heat’ balance) is usually very important; few food processes do not employ heat at some stage. In many instances (freezing, evaporation, pasteurisation) the addition or removal of heat is the substance of the manufacturing process and may involve very considerable quantities of energy. Only when the material and energy balances are complete can the detailed design or specification of process equipment begin.