Edible rendering processes are basically meat processing operations and produce lard or edible tallow for use in food products. Edible rendering is generally carried out in a continuous process at low temperature (less than the boiling point of water). The process usually consists of finely chopping the edible fat materials (generally fat trimmings from meat cuts), heating them with or without added steam, and then carrying out two or more stages of centrifugal separation. The first stage separates the liquid water and fat mixture from the solids,. The second stage further separates the fat from the water. The solids may be used in food products, pet foods, etc, depending on the original materials. The separated fat may be used in food products, or if in surplus, it may be diverted to soap making operations. Most edible rendering is done by meat packing or processing companies.
An alternative process cooks slaughterhouse offal to produce a thick lumpy stew which is then sold to the pet-food industry to be used principally as tinned cat and dog foods. Such plants are notable for the offensive odour that they can produce and are often sited well away from human habitation.