What you don't know about puffing and extrusion

The material containing a certain amount of moisture is pushed by the screw in the sleeve of the extruder and blocked by the discharge abrasive and the shut-off device in the sleeve. Heating, so that the material is at a high temperature of 3 ~ 8MPa and 120 ~ 200 ℃, and can reach a higher temperature according to needs.

Since the pressure exceeds the saturated vapor pressure at the extrusion temperature, the material will boil and evaporate of moisture in the extrusion cylinder. Under such high temperature, shear force and pressure, the material is in a molten state. When the material is forcibly squeezed out of the die mouth, the pressure suddenly drops to normal pressure, and the water flashes at this time, resulting in a situation similar to "explosion", and the product expands accordingly.

The moisture evaporates from the material and takes away a lot of heat, so that the material instantly drops from the high temperature during the extrusion process to a relatively low temperature of 80°C. Due to the decrease in temperature, the material is solidified and formed from the state when extruded, and maintains the puffed shape.

The ingredients of extruded puffed food are mainly starch. Therefore, the formation of the puffed state is mainly completed by starch. In the state of high temperature and high pressure, starch granules first gelatinize, and then the molecules are combined and cross-linked under the action of high temperature and high shear to form a network structure. After extrusion, cooling and solidification, the structure becomes the skeleton of the puffed food structure, and the ingredients from other raw materials are filled in it. Therefore, the content of starch in the raw material directly affects the puffing degree of the product. In the absence of starch in the raw material, the puffing effect is basically not produced.

Features of extrusion technology

1) Improve practical quality, easy to store

The use of puffing technology can make corn and sorghum, which originally contain more cellulose and vitamins, become bulky and soft, and the Maillard reaction generated during the puffing process increases the color, aroma and taste of the food. Thereby, the practical quality is improved, and the food has a unique flavor of light body, crispness and rich aroma.

2) Improve product quality and reduce harmful substances

The extrusion process is typically a high temperature, high pressure, short time process, which results in limited material handling and thus retains almost all the nutrients in the raw material in the final product. At the same time, the high temperature short time process can still reduce undesirable product factors like harmful enzymes and microorganisms.

3) Wide applicability of raw materials and variety of products

There are many kinds of raw materials that can be processed. It can not only deeply process grains, potatoes, beans and other grains, make coarse grains and produce exquisite snacks, but also process fruits and vegetables, spices and some animal proteins. When producing puffed food, products with different shapes can be produced by using the same extruder only by changing the raw materials and the die.

4) High production efficiency and low production cost

The large twin-screw extruder has a production capacity of tens of tons per hour and is easy to operate. Compared with the traditional cooking method, using modern extrusion technology to process products has significantly reduced time consumption, energy consumption, labor force, and plant occupation.

5) Less waste and no waste

When using starch to make wine and candy, after the raw materials are expanded, the utilization rate is over 98℅, the sugar yield is increased by 12℅, and the wine yield is increased by 20℅. In addition, in general, apart from the need for a small amount of raw materials as primers when starting up and shutting down, almost no waste is discharged during the entire production process, and there is no waste of raw materials.

Extrusion puffing equipment

The extruder was developed from a simple molding machine, initially only used in the plastics industry, and later in the food and other industries. The extruders currently used are mainly screw extruders, which can be divided into two types: single-screw and twin-screw according to the structure.

The single-screw extruder propels the material by a screw that gradually increases from thin to thick and the pitch from wide to narrow. At present, the single-screw extruder produced in my country basically adopts a screw with a shallow thread height, and the rotation speed is 300-400 r/min. It can generate high grinding and high shearing force, and the time the grain raw material stays in the barrel is only In 10-20s, the temperature of the material before ejection is as high as 130-140℃.

 The twin-screw extruder has a pair of counter-rotating or co-rotating screws that are continuously meshed with each other, and the material is forcibly conveyed by the principle of positive displacement. In the process of material conveying, pressure backflow is rarely formed, which can make the local pressure rise sharply, speed up the puffing process, and obtain high output.