Classification of extrusion technology

Due to the different expansion processes, it can be divided into direct extrusion expansion and indirect extrusion expansion.

Direct extrusion expansion technology

Working principle: The materials with certain moisture content and starch content are pushed by the screw in the sleeve of the extruder, blocked by the discharge die (or the throttling device in the sleeve), and heated from the outside, or heated by the friction heat between the materials and the screw, between the materials and the sleeve, so that the materials are at a high pressure of 3 ~ 8 MPa and a high temperature of about 200℃. Such a high pressure exceeds the saturated vapor pressure at the extrusion temperature, so the water in the extruder sleeve will not boil and evaporate. At such a high temperature, the material will be in a molten state. Once the material is extruded through the die, the pressure suddenly decreases, the water evaporates sharply, and the product expands accordingly. The loss of water takes away a lot of heat, which makes the temperature of the material drop to 80℃ instantly. C, curing and molding the product to obtain a direct extrusion puffed product. The technological process of direct extrusion expansion technology mainly includes:

Feeding (extrusion), puffing, cutting, drying, packaging and finished products.

Indirect extrusion expansion technology

Working principle: raw materials are cooked in an extruder, and when the temperature is lower than 100℃, the raw dough is formed at low temperature, which can prevent the water in the material from instantly turning into steam and expanding. The expansion process of products is mainly accomplished by baking or frying after extrusion. In this process, after the raw materials pass through the extruder, only the raw materials are allowed to ripen and semi-ripen, and the products are given a certain shape. At the same time, in order to improve the quality of products, make the texture of products more uniform and gelatinize more thoroughly, the extruded semi-finished products need to be kept at constant temperature and humidity for a period of time, and then baked or fried in the later stage. The technological process of indirect extrusion technology mainly includes:

Feed blank, dry, expand, package and expand food.

Compared with direct extrusion puffed food, indirect extrusion puffed food generally has the characteristics of uniform structure, good taste, less sticky teeth, complete starch gelatinization and easy control of puffing degree, and is a popular puffed food.