According to the law of conservation of matter, mass cannot be destroyed; it can only be converted from one form to another. This principle allows us to account for all the material that enters and exits a food processing operation or even the entire plant. The mass of incoming materials must be accounted for in either the product exiting the plant or in waste streams. Furthermore, the mass of individual components (water, protein, fat, etc.) must also be balanced within the process. That is, all of the protein (or sugar, water, etc.) must be balanced between the inputs and outputs. In fact, any individual specific component (any molecular species) must be balanced in a unit operation.