Extrusion is a means of shaping something by forcing it through an opening.

        In food processing, extrusion combines heating with the act of extrusion to create a shaped cooked product. Extrusion is accomplished by single screw extrudersand twin screw extruders.The choice of extruders is determined by the moisture content of the extrusion feed mixture. Low moisture extrusion mixtures appropriate for a single screw extruder must have a feed composition of less than 35% moisture. High moisture extrusion mixtures, those with a moisture level of 35% or above, require the use of a twin-screw extruder.The 13.5% (w/w) moisture content of the extrusion mixtures used throughout this study was applicable to a single screw extruder.