Fish products and Byproducts Technology

Unit 6 - Extrusion

6.6.2. Twin screw extruder
A twin-screw extruder has two screws running in parallel with intermeshing flights for increased performance. Expansion of the ingredients is still limited without the introduction of additional heat and moisture. These extruders are therefore normally supplied with either a water mixer or steam conditioner for superior gelatinisation and expansion, by raising the moisture content of the mix to 20-25% prior to entering the extruder, or in the case of steam extrusion, the temperature of the material is also increased to approximately 55-65ºC prior to entering the extruder barrel. This is controlled using metering systems and injected either into the preconditioner or sometimes directly into the barrel of the extruder. A higher amount of thermal energy can be supplied in this way in addition to the mechanical energy needed to cook the product.
Types of twin screw extruder

• Non intermeshing twine screw extruders
• Counter rotating twine screw extruder
• Co-rotating twin screw extruders