Rendering and Hot Water Extraction

Rendering is the process of extraction of fat from animal tissue by application of heat. Rendering is also called trying. During rendering fat cells are ruptured, expelled and water evaporated. The accompanying connective tissues are separated as solid residue called cracklings. Rendering can be done by following two methods;

  1. Wet rendering
  2. Dry rendering

Wet rendering:

Fig: Autoclave for wet rendering

wet rendering has application of steam for extraction of fat from fatty tissue. Fatty tissue is chopped and digested in an autoclave at 120 – 130°C. The fat that separates out from disintegrated tissue is collected and the water is removed by centrifugation and evaporation. The fat (lard) is usually further processed to remove color, free fatty acids and unwanted odor.

Fig: Flowchart for wet rendering of fatty tissue



Dry rendering:

Fig: Autoclave for dry rendering

dry rendering involves cooking of meat scraps under vacuum in steam jacketed kettles. The heat is transferred indirectly by conduction. The heat and pressure gradients that develop inside the vessel cause fat to leach out. These also lead to denaturation of protein and removal of water. The fat is finally freed from residual water by evaporation and proceed further for purification.

Fig: Flowchart for dry rendering of fatty tissue

Use of lard: these are used as Shortening in bakery. It is also used as raw material for margarine preparation and is principle source of fat used in sausage.

Use of tallow:  it is Inedible but have Industrial use such as boot polish, glue, cosmetics and grease etc.

Shortening; these compounds break the network of gluten in food so that bite is shortened, i.e. easy bite.  Example; ghee, butter, fat etc.

Extraction of oil from oil bearing fruits:

Hot water extraction method is used for obtaining oil from fruits like coconut, palm, avocado by application of hot water.

Fig: Flowchart for extraction of oil from oil bearing fruits




About Author

Name : Pratiksha Shrestha

Ms. Shrestha holds masters degree in food engineering and bioprocess technology from Asian Institute of Technology (AIT) Thailand. She is currently working for Government of Nepal at Department of Food Technology and Quality Control (DFTQC), Kathmandu. She is also a teaching faculty in College of Applied food and Dairy Technology (CAFODAT) affiliated to Purbanchal university, Nepal.