Food extrusion

Extrusion in food processing consists of forcing soft mixed ingredients through an opening in a perforated plate or die designed to produce the required shape.

The extruder is typically a large, rotating screw tightly fitting within a stationary barrel, at the end of which is the die.

Products made through extrusion cooking include many breakfast cereals and ready-to-eat snacks, confectionery, some baby foods, full-fat soy flour, textured vegetable protein, some beverages, and dry and semi-moist pet foods.

In the extrusion cooking process, raw materials are first ground to the correct particle size, usually the consistency of coarse flour.

The dry mix is passed through a pre-conditioner, in which other ingredients are added depending on the target product; these may be liquid sugar, fats, dyes, meats or water.

The extruder is a large, rotating screw tightly fitting within a stationary barrel, at the end of which is the die.

[citation needed] Cooking takes place within the extruder, where the product produces its own friction and heat due to the pressure generated (10–20 bar).

[citation needed] Moisture is the most important of these factors, and affects the mix viscosity, acting to plasticize the extrudate.

[4] Dry pasta has been produced by extrusion since the 1930s,[2] and the method has been applied to tater tots (first extruded potato product: Ore-Ida in 1953).

[4][5] In 1963, the USDA and UNICEF tested a full fat soy flour produced from extrusion-cooked soybeans as a source of nutrients for children.

[7] Extrusion enables mass production of some food, and will "denature antinutritional factors"[1] while destroying toxins or killing microorganisms.

It may also improve protein quality and digestibility[1] and affects the product's shape, texture, colour, and flavour.

[8] Nutritional quality has been found to improve with moderate conditions (short duration, high moisture, low temperature), whereas a negative effect on nutritional quality of the extrudate occurs with a high temperature (at least 200 °C), low moisture (less than 15%), or improper components in the mix.

[1] Directly expanded types include breakfast cereals and corn curls, and are made in high-temperature, low-moisture conditions under high shear.

Specific examples include cheese curls, macaroni, Fig Newtons, jelly beans, sevai, and some french fries.