Food Extruder Machine

Food extruder machines have a very long history, with meat extruders being used to make sausages as early as the 1870s. Since then, food extrusion technology has found its way into everyday kitchen appliances, such as herb and coffee grinders, meat grinders, and pasta machines. These devices enable consistent quality, uniformity and efficient output when mass-producing edible products. Raw materials can be processed into cooked or cold-formed consumer products in a variety of sizes, colors, shapes and textures. Foods that are high in starch can be extruded well, such as pasta, bread, cereals, snacks and candies. Food extruders use the heat generated by the friction of the process, as well as any additional cooking heat provided, to evenly mix the ingredients before passing the material through a mold to form the final product.

On the surface, the principles of operation of the food extrusion are similar in all types. First, the raw materials are fed into the extruder barrel and the screw(s) then convey the food to it. Further down the barrel, there are smaller flights that will restrict the volume and increase the resistance to movement of the food. As a result, the barrel gets filled and the spaces between the screw flights and becomes compressed. As it moves further along the barrel, the screw will knead the material into a semi-solid, plasticized mass. The hot extrusion process involves heating above 100ºC. In this case, the frictional heat and other additional heating process make the temperature to rise rapidly.Also, the smaller flight section of the barrel increases the pressure and shearing. Finally, the entire content is forced through one or more restricted openings (dies) at the discharge end of the barrel. When the food emerges under pressure from the die, it expands to the final shape and then cools rapidlyby flashing off moisture as steam. Here, a variety of shapes, rods, spheres, doughnuts, tubes, strips or shells can be formed.

The main application of cold extruders is in pasta production, although similar machines are used to form biscuit dough into different shapes. A pasta extruder is used to make many different types of pasta using dough made from durum wheat flour (or ‘semolina’) and eggs (optional). Coloured pasta can also be made by adding tomato purée or spinach paste etc. Different sizes of equipment are available, from small manual machines that are used in micro-scale production and food service outlets, to larger electric machines. The equipment has a mixing chamber, extruder barrel and a die for the desired pasta shape. There is debate over the best material for dies, with some equipment manufacturers using stainless steel or plastic, and others preferring bronze dies, which they claim imparts a rough surface to the pasta that holds sauce better than pasta made by other methods. Shapes are cut to the appropriate length as they emerge from the die, except rigatoni, which is extruded in long lengths and then cut to the correct size (straight for rigatoni or angled for penne rigati). Pasta is cooked immediately in food service outlets, or dried by processors for retail sale. It can also be frozen for up to six months.

Extruders may be single- or twin- screw machines. Twin-screw machines have approximately twice the capital and maintenance costs of single screw machines and are unlikely to be affordable by most small -scale processors as compared to single- screw extruders. The two factors that control the type and quality of foods that are produced by hot extrusion are the operating conditions in the extruder barrel and the mixture of ingredients that is used.