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.
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.
Steam rendering for animal fat
