Rendering

See also computer rendering and artistic rendering.

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Rendering is a process by which animal fats are purified. There are important differences between kitchen rendering and industrial rendering.

Rendering in the kitchen

In the kitchen, "rendering" can mean "clarifying" butter into ghee, suet into tallow and bacon fat into lard. Rendering involves melting and extended simmering, followed by filtering and cooling. The entire process is then repeated in a clean vessel. Unlike raw animal fats, rendered animal fats can be stored for extended periods without refrigeration, provided they are kept in airtight containers to prevent oxidation.

Industrial rendering

Industrial rendering is a factory-scale process that uses slaughterhouse waste, restaurant grease, and butcher shop trimmings as its raw materials. This material can include the fatty tissue, heads, bones, offal, and other waste animal parts. The rendering process simultaneously dries the material and separates the fat from the bone and protein. After rendering, the materials are much more resistant to spoiling. The fat can be used in animal feed, in soap-making, in candles, as a raw material for biodiesel production, and as a feed-stock for the oleochemical industry. The bone and protein becomes dry particles known as meat and bone meal. For many years meat and bone meal were fed to cattle. This practice is now prohibited in developed countries because it believed to be the main route for the spread of BSE (mad-cow disease).