Rendering (animal products)

Rendering is a process that converts waste animal tissue into stable, usable materials. Rendering can refer to any processing of animal products into more useful materials, or, more narrowly, to the rendering of whole animal fatty tissue into purified fats like lard or tallow. Rendering can be carried out on an industrial, farm, or kitchen scale. It can also be applied to non-animal products that are rendered down to pulp. The rendering process simultaneously dries the material and separates the fat from the bone and protein, yielding a fat commodity and a protein meal. In animal products, the majority of tissue processed comes from slaughterhouses, but also includes restaurant grease, butcher shop trimmings, expired meat from grocery stores. This material can include the fatty tissue, bones, and offal, as well as entire carcasses of animals condemned at slaughterhouses and those that have died on farms, in transit, etc. The most common animal sources are beef, pork, mutton, and poultry. The rendering process varies in a number of ways: Whether the end products are used as human or animal food depends on the quality of input material and the processing methods and equipment. The material may be processed by wet or dry means. In wet processing, either boiling water or steam is added to the material, separating fat into a floating phase. In dry processing, fat is released by dehydrating the raw material. The temperature range used may be high or low. Rendering may be done either in discrete batches or in a continuous process. The processing plant may be operated by an independent company that buys input material from suppliers, or by a packing plant that produces the material in-house. 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).