Rendering este extragerea grasimilor prin incalizire si/sau presiune
Render - The free diction
To reduce, convert, or melt down (fat) by heating.

Fats and Oils Formulating and Processing for Applications, Third Edition
By Richard D. O'Brien

Animal fats are recovered from fatty tissues by cooking processes, known as rendering. The two predominant rendering processes arc wet and dry rendering. Wet rendering produces the better quality oil while dry rendering produces the best quality protein. The wet process is preferred for edible animal fats and the dry process for inedible products. Regardless of the process used, the materials from the meatpacking plant to be rendered are broken up into small pieces (2 to 5 cm) with a crusher or pre-breaker. The pieces are then cooked in batch or continuous cookers with agitation to evaporate the moisture, break down the fat cells, and release the fat.


2.2.3.1 Wet Rendering

The two varieties of wet rendering are low temperature, which is conducted at temperatures up to the boiling point of water, and high temperature or steam render¬ing, which is carried out under pressure in closed vessels. Most of the edible animal fat produced in the United Stales is rendered by the steam process. The typical equipment used is a vertical cylindrical steel vessel with a cone bottom, designed for a steam pressure of 40 to 60 psi 42.7 to 4 bar) and a corresponding high temperature. The vessel is filled with the fatty material from the cooking operation plus a small amount of water, and steam is injected to boil the water and displace the air. The vessel is then closed, except for a small vent, and steam injection is continued until the operating temperature and pressure are attained. Under these conditions, the fat separates from the solids and rises to the top of the vessel. The pressure is then released and the fat is drawn off and purified by settling or with a centrifuge.

2.2.3.2 Dry Rendering

Dry rendering involves cooking the material at 115 to 120°C (239 to 248°F) in agitated, steam-jacketed vessels until the moisture has evaporated, usually 1.5 to 4 hours. No steam is injected into the fatty material during processing us with the wet process. The cooked material is then screened to drain off the free fat before pressing the high-protein solids to separate the remaining 6 to 10% residual fat. The fats accumulated are then centrifuged or filtered.