In general there are two different rendering systems established worldwide. Depending on whether the animal fat is gained from an already dried material or from a wet phase, the systems are named dry and wet rendering, respectively. There is no general rule when and where wet or dry rendering is preferred, but it can be observed that wet rendering is mostly used where heat-sensitive, high-value products like fish oils, edible fats or poultry fats are produced.
The fat melting and rendering processes aim at three important goals -
• Removal of water to get stable products which are fat and solids, e.g. proteins
• Separation of the dry product into fat and solids (protein)
• Sanitation, i.e. the reduction of possible pathogenic loads, which is the less important the fresher the processed material is.
Some of the equipment used in the process is illustrated in Figures 4-7 and 9-10.