Extrusion

A “Master Chef”.

An extruder is effectively a high-performance cooking pot with ultra-effective stirrer and giant strainer in one, extending over several meters. The term extrusion generally denotes forcing a substance out through a die. A meat mincer, for instance, could in principle be regarded as an extruder. Extruders are made up of one or more screws in a tightfitting barrel. At one end raw material is fed in and at the other end the product is forced through a die and possibly chopped up. In between, the mash to be extruded is processed thermally by the heating system of the barrel and mechanically by the geometry and rotational speed of the screws.

The dry raw materials – for instance rice, wheat or potato flour – are mixed with water or hot steam and other ingredients such as salt or even cocoa powder in the preconditioner and precooked. The ingredients then enter the screw, where they are exposed to the action of heat, mechanical force and time – just as happens on a small scale in any kitchen. However, in the extruder the heat is primarily produced by “agitating”, that is by mechani - cal energy. The “dough” is firmly compressed by rotation of the screws, rubbed open as it were, and so heated.

The rotational speed of the two screws and the shear forces determine the temperature and degree of gelatinization of the product and thus its texture and quality. Raw product composition is, however, also a factor. Rice, for instance, makes the product harder, while adding more wheat softens the dough strand forced out of the end of the die. High torques, fast screw speeds and high pressures in the extruder offer greater leeway for par - ameter optimization. However, product quality is not only dependent on the structure of the extruder but above all on the skill and experience of the operator.

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