What Is Extrusion Cooking?

Extrusion technology, well known in the plastics industry, has now become a widely used technology in the food processing industry, where it is referred to as extrusion cooking. It has been employed for the production of so-called engineered food. Extrusion cooking is a process by which a set of mixed ingredients are forced through an opening in a perforated plate or die with a design specific to the food, and is then cut to a specified size by blades. The machine which forces the mix through the die is an extruder. The extruder consists of a large, rotating screw tightly fitting within a stationary barrel, at the end of which is the die. The product exits the extruder through a die where it usually puffs and changes texture from the release of steam and normal forces. The extrusion is a high-temperature, short-time process that minimises losses in vitamins and amino acids. Colour, flavour and product shape and texture are also affected by the extrusion process. One of the advantages of extrusion cooking is versatility with regard to ingredients selection and the shapes and textures of products that can be produced. Extrusion also has the following beneficial effects: a) destruction of certain naturally occurring toxins, b) reduction of microorganisms in the final product, c) improvement of protein quality and digestibility, and d) reduction of moisture content in the final product.