Extrusion

ExtrusionExtrusion A continuous process by which moistened, expansible, starchy, and/or proteinaceous materials are plasticized and cooked by a combination of moisture, pressure, temperature, and mechanical shear. ExtruderExtruder A tool used to introduce thermal and mechanical energy to food and feed ingredients, forcing the basic components of the ingredients, such as starch and protein, to undergo chemical and physical changes and form a predetermined shape

Cross sectional view of a extruder

Extrusion cooking is a modern high temperature short time processing Purpose of extrusion cooking are as follows Sterilization Expansion Dehydration Stabilization Extrusion cooking is a modern high temperature short time processing Purpose of extrusion cooking are as follows Sterilization Expansion Dehydration Stabilization Extrusion cooking

Extruded products

Extrusion processing steps Ingredients are propelled along the barrel of the extruder by one or two screws. The mechanical screw action and the friction it creates blends, shears and cooks the material (Held at ºC for about 30 seconds). At the end of the barrel, the mixture is forced through a die at high pressure. Due to the difference between pressure inside and outside of the barrel, the material expands, and according the die shape and the cutter blade action, it creates a pellet of varying size, shape and density. Ingredients are propelled along the barrel of the extruder by one or two screws. The mechanical screw action and the friction it creates blends, shears and cooks the material (Held at ºC for about 30 seconds). At the end of the barrel, the mixture is forced through a die at high pressure. Due to the difference between pressure inside and outside of the barrel, the material expands, and according the die shape and the cutter blade action, it creates a pellet of varying size, shape and density.

Types of extruders There are three major types of extruders: 1.Piston extruders 2.Roller extruders 3.Screw extruders There are three major types of extruders: 1.Piston extruders 2.Roller extruders 3.Screw extruders Based on the no of screw in the barrel: Single screw extruder Twine screw extruder Based on the no of screw in the barrel: Single screw extruder Twine screw extruder

Piston extruder: consist of single piston or multiple sets of pistons that deposit a process amount of product on to conveyers or trays. Roller type extruder : They are used to form the shape of a product. A roller consis of two counter rotating roller that either turn at similar or differential speeds. This process is also referred as calendaring in that dough industry Screw extruders :Utilize single, twin or multiple screws rotating within a metal cabinet called the barrel. The screws convey the material formed and though a small orifice called die which can take on many shapes and sizes

Single screw extruder : The single screw extruder is an entry-level machine for small- scale operations. A large proportion of the expanded animal feed and modified raw materials such as soya bean and corn for feed purposes use single screw extrusion. Single screw extruder : The single screw extruder is an entry-level machine for small- scale operations. A large proportion of the expanded animal feed and modified raw materials such as soya bean and corn for feed purposes use single screw extrusion. Twin screw extruder : A twin-screw extruder has two screws running in parallel with intermeshing flights for increased performance. Twin screw extruder : A twin-screw extruder has two screws running in parallel with intermeshing flights for increased performance.