This is often accomplished using a filter press with a filter aid, such as diatomaceous earth. Centrifuges may be used in large operations, but are expensive. The final step in extraction is drying. The combination of water and air will cause the extracted fat to break down. Therefore, the oil must be dried immediately after washing.
Flash drying is the most popular method of drying.
The fat is heated quickly to high temperatures, and then pumped into a tank where the water escapes as a vapor which is collected in another tank. Temperatures can be reduced if carried out under a vacuum. Rendering results in crude oil, which is then further refined. The amount of refining required depends on the intended use of the final oil. The first step of refining is neutralization.