Animal fat processing: steam rendering

Nearly all animal fats, tallow or beef fat and lard, are obtained bv rendering. The two predominant rendering processes are wet and dry rendering. Wet rendering produces the better quality oil while dry rendering produces the best quality protein.

Most of the edible animal fat produced in the United States is rendered by the steam process. In the steam rendering of high fat stock, 99.5% or more of the fat in the raw material is ordinary recovered.

The apparatus used is a vertical cylindrical steel autoclave or digester with a cone bottom, designed for a steam pressure of 40 to 60 pounds per square inch and a correspondingly high temperature. The comminuted fatty tissues are first heated to 50 °C – 60 °C and then quickly to 80 °C - 90 °C with direct steam.

Animal fat

The vessel is filled with the fatty material plus a small amount of water and steam is admitted to boil the water and displace the air.

The vessel is then closed except for a small vent, and the injection of steam is continued until the operating temperature and pressure are attained; then digestion is continued for a variable time depending upon the temperature and also the nature of the charge.

The usual digestion time is 4 to 6 hours. The process dissolves the tissue releasing the fat from proteinaceous material. The liquid fat floats on the top water, which can be separated thereby producing edible fat products where color, flavor and keeping quality are of great importance.
Animal fat processing: steam rendering  

Processing of animal fats

For centuries animal fat was the principle edible source. Handing and processing animal fats have evolved from the primitive to state-of-the-art processing equipment and technology. Processing of animal fat for edible use may ranges from simple to complex.

If fat is selectively removed from the animal carcass and carefully rendered, the result product can be simply filtered to remove particulate.

For more complex products with more rigorous quality specifications, the complete processing train of caustic refining, bleaching, hydrogenation, blending and deodorization is used.

Animal fats recovered from fatty tissues by cooking processes known as rendering. The two predominant rendering processes are wet and dry rendering.

In wet rendering, the fatty tissue is heated under steam pressure, thus rupturing the cells and liberating the fat.  The lard produced by this method of rendering is known as ‘prime steam lard’. In addition to lard, tallow and whale oil also usually steam rendered. The wet process is preferred for edible animal fats.

In dry rendering, the fatty tissue is heated in jacketed drums with agitation until the fats is released. Presently, centrifuges are used to separates the fat from water and protein. The dry rendering process is preferred for inedible products.
Processing of animal fats