Extrusion and its characteristics
Extrusion is a baking process based on high pressure (34 to 37atm), controlled humidity (20 to 30%) and high temperature (125 to 150ºC), generating an increment of digestibility in relation to the raw mixture, besides resulting in a product With desired final appearance.
The extrusion process has gained space in food production due to its versatility, high thermodynamic efficiency, low operating cost and low space per metric unit of production, although it requires high cost equipment that is compensated by the better food efficiency of the products Produced. In addition, the extruded animal feed industry has made it possible to use high-efficiency by-products from food-producing industries, such as refrigerators, grain crushers, and others. In this way a harmonic chain was created, transforming, improving and efficiently using what was previously seen as specific endless products and even as environmental problems.
There is a huge variety of products that can be used in the extrusion process. These products should be designed to provide adequate nutritional balance and organoleptic characteristics at a cost that may be lower than other thermal processes.
The extruder assembly consists basically of:
Feed system: this system is essential in the extrusion process, it must be constant and capable of uniformly feeding dry, liquid or mixed ingredients. Silos are used for storage of dry ingredients. The dry portion of the food is added through a feed screw system capable of delivering a uniform flow rate at any desired extrusion rate.
Pre-conditioner: place where the raw mixture is cooked through the addition of moisture and heat (steam and water). It is in the pre-conditioner that the application of much of the thermal energy used in the extrusion process occurs.
Extruder Cylinder: The pre-conditioned (pre-baked) mixture is continuously discharged directly into the extruder cannon, which has cylinder segments (called liners) and threads. Through this suitably configured set of threads and sleeves that most of the mechanical energy used in the process is applied, and this occurs continuously, where the sets of threads will convey and print pressure and shear to the material against the formatter array.
Matrix: has known holes according to the size of the desired food. This will determine the size and shape of the final product as well as the amount of mechanical energy required for the product to pass through a larger or smaller outlet area.
Set of knives: this is fixed to the matrix and coupled to a cart gives it sustainability and rotation through an electric motor to cut the food to the desired size.
Pneumatic tube: cylindrical tube, driven from an exhaust system, provoking a suction system, which transports the food in the desired and still wet granulometry, to the conveyor belts.