Extrusion is a process where material is forced through a die to shape it, used in home and manufacturing. Examples include piping bags, pasta makers, and metal, plastic, ceramic, and food products. Extruded foods are a specialty of food science, but there is debate over their nutritional quality.
Extrusion, from the Latin past participle extrudere meaning “to expel”, refers both to the process in which material is forced through a die or series of dies to shape it, and to the product of that operation. The process is used in the home and in manufacturing. Shapes most often produced this way include round objects such as pipes, rods and tubes, rectangular objects such as solid and hollow bars, and plates. The term also refers to the outpouring of lava from a volcano.
At home, the most familiar example of an extrusion might be the sac à poche. Used for forming cookies and for icing cakes, the piping bag extrudes the icing or dough through a tip that shapes the output. This is done in short bursts to quickly produce a series of identical objects. Kitchen equipment that makes pasta or sausage can also be equipped with an extruder that shapes the finished product. A very popular extruder toy is sold with modeling compound, where a user selects a mold and slides it onto the front of the machine, inserts the soft material, and presses the handle to produce long or short pieces of clay in the desired shape.
In manufacturing, extrusion is used with a variety of materials, including metal, plastic, ceramics, and food. Different materials undergo this process to make different types of products. Copper is extruded to make pipes for plumbing, while aluminum is used to make things like window frames, rails, and railings. Steel is extruded into rails or rods, and some titanium airplane parts are produced this way. Plastic extrusion results in a number of shapes, including cylindrical tubes, pipes and rods, rails, and very thin rectangular surfaces that are characterized as sheets or films.
Food manufacturing uses extrusion in ways that are beyond what is possible in the standard home kitchen. Curls of cheese and other snacks, pastas, cereals and nutrition bars are all made with this process, as are numerous pet foods. In fact, extruded foods are a specialty of food science, and scientists with training and experience in this particular area of food production oversee these processes. There is debate whether preparing food in this way, at least in some cases, reduces the nutritional quality of the product.
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