The Rendering Process

In batch cooking, a vessel is filled with raw material and sealed. The material is processed under controlled conditions using times and temperatures related to the type of raw material. The cooked material's temperature ranges from 250°F to 275°F. It is discharged to the percolator drain pan where a perforated screen allows the fat to drain away from the protein solids, also known as tankage. After about one hour of draining, the solids still contain about 25% of fat. They are conveyed to the screw press to complete the separation of fat from solids. The final protein solids have residual fat content of 9% to 13%, which varies from the content of the raw material, such as beef, poultry and fish. The protein solids are known as cracklings, which are then screened and ground with a hammer mill to produce protein meal. After the product is discharged, the cycle is repeated.

The first continuous rendering system was developed in the early 1960s. With this method, the raw material is fed semi-continuously to the cooker and the cooked material is discharged at a constant rate. A continuous rendering system normally consists of a large cooking unit, whereas the batch system consists of one to 12 smaller cooking units. This system usually has a higher capacity than the batch cooking process and enables more material to be processed in less time.