Pasta extruders
Introduction
Extrusion in food processing involves forcing soft mixed ingredients through an opening in a perforated plate or die (cutting die) designed to produce the required shape. The extruded food is then cut to a specific size using blades. The machine that forces the mixture through the die is known as an extruder, and the mixture is known as extruder. The extruder is usually a large rotating screw that fits tightly inside a stationary cylinder, at the end of which is the die.
Extrusion allows food chain production through a continuous and efficient system that guarantees the uniformity of the final product. These include some pastas, breads (croutons, breadsticks, and flatbreads), many breakfast cereals and ready-to-eat snacks, candy, pre-made cookie dough, some baby foods, whole soy, textured vegetable protein, some beverages, and dry and semi-moist pet foods. Food products manufactured by extrusion usually have a high starch content.
Process
In the extrusion process, raw materials are first ground to the correct particle size, usually the consistency of coarse flour. The dry mixture is passed through a preconditioner, in which other ingredients are added depending on the destination product; These can be liquid sugar, fats, dyes, meats or water. Steam is injected to start the cooking process and then the preconditioned mixture (extrudate) is passed through an extruder. The extruder is a large rotating screw that fits tightly inside a stationary cylinder, at the end of which is the die.[1] The rotating screw of the extruder forces the extrudate into and through the die. The extrudate remains in the extruder during the residence time.
Many extruded products swell and change texture as they are extruded due to reduced forces and the release of moisture and heat.[1] The extent to which this does is known as the expansion ratio. The extrudate is cut to the desired length by blades at the exit of the extruder, which rotate around the die openings at a specific speed. The product is then cooled and dried, becoming rigid but maintaining porosity.
Cooking takes place inside the extruder, where the product produces its own friction and heat due to the pressure generated (10-20 bar). The process can induce both protein denaturation "Denaturation (biochemistry)") and starch gelatinization under some conditions.
Many food extrusion processes involve a high temperature for a short period of time.[1] Important factors in the extrusion process are the composition of the extrudate, the screw length and rotation speed, the temperature and humidity of the barrel, the shape of the die, and the rotation speed of the blades. These are controlled depending on the desired product to guarantee uniformity of the result.