2. Definitions and principles

2.1 What are extrusion, coextrusion, bake-extrusion, bake-extrusion-expansion?

Extrusion, from the Latin extrudere meaning "to push out", is a unitary processing operation that consists in forcing a product through a small orifice - the die - under the action of high pressures obtained by means of an Archimedes screw (in the case of the single-screw extruder) or two screws (in the case of the twin-screw extruder). This is a continuous process, enabling the production of a wide variety of products in terms of physical structure, composition and functional properties. Depending on the technique used, the operation may encompass various functions: material transport, mixing, compression, kneading, shearing, chemical/enzymatic reactions, degassing, heating, cooling, baking, sterilization,...