Vacuum drying process is to place the dried material in a closed drying chamber, vacuum pumping system is used while heating the dried material continuously, so that the moisture in the material diffuses to the surface through pressure difference or concentration difference, and the water molecule obtains enough kinetic energy on the surface of the material. After overcoming the mutual attraction between the molecules, it escapes to the low-pressure space of the vacuum chamber and is thus heated. Vacuum pump pumping process. Vacuum drying can easily recover useful and harmful substances, and can achieve good sealing. In the sense of environmental protection, vacuum drying is called “green drying”.
In vacuum, the boiling point of material moisture decreases and the vaporization process accelerates, so it is especially suitable for materials sensitive to temperature and easy to decompose. Vacuum drying is mainly carried out in low vacuum area. In the process of grain moisture vaporization, its boiling evaporation temperature is proportional to the ambient pressure. The high moisture grain is placed in a sealed drying cylinder to form and maintain a certain degree of vacuum. At the same time, the grain in the drying cylinder is heated continuously, so that the moisture in the grain diffuses to the surface through the pressure difference. After vaporization, it is pumped out by a vacuum pump to realize continuous pairing in vacuum and low temperature. High moisture grain is dehydrated and dried. Vacuum drying reduces the boiling evaporation temperature of water from 100 C to below 40 C. Because the evaporation temperature is lower than the gelatinization temperature of starch, the grain will not be damaged. It avoids the expansion of grain and bursting waist, and ensures the quality of grain after drying. It guarantees that the original color, aroma, taste, nutrient composition and quality of the material are basically unchanged after drying. It is a real low-temperature drying, which is completely different from the general hot air low-temperature drying.
Vacuum freeze drying technology is to freeze the material first, then heat up under vacuum conditions, so that ice sublimation to achieve the final drying purpose. The heating methods adopted include infrared heating and microwave heating. The heat provided should not only sublimate the ice quickly but also damage the surface of the product. Vacuum freeze-drying technology can keep food fresh by vacuum atmosphere in the past 20 years. The packaging technology has developed rapidly. Because this kind of packaging not only has the characteristics of free oxygen to make food not easy to decay and deteriorate, fitted and inflatable packaging can not be harmed by insects and can inhibit the growth of mould, can improve and prolong the degree of food preservation and storage time, but also has the advantages of simple structure, easy operation, low price, low cost, elegant appearance and easy popularization of plastic packaging materials. There are many kinds of food in vacuum packaging, such as mustard pickles, turnips, kelp, sausage, grilled chicken, roast duck, soybean products, milk powder, wheat milk essence and so on. Because fresh products go through a long period of time from harvesting to reselling, it is easy to increase the selling price because of the serious loss. The promotion of vacuum packaging technology will reduce the price and refrigeration cost of fresh products, thus alleviating the spearhead between supply and demand. Therefore, vacuum preservation will become a potential market and be active in people’s lives.
Vacuum freeze-drying technology first appeared in the early twentieth century, and has developed rapidly in recent years. This is because it has many advantages compared with the usual hot sun, hot air drying, infrared drying and high frequency drying. Because the freeze-drying process is to freeze the dry material first, and then vacuum, so that the frozen water in the material does not go through the liquid and directly sublimate to remove. Therefore, the freeze-dried products can not only show the porous state and keep the original shape, so that they can easily restore to their original state after adding water, but also prevent the thermal decomposition of materials by low temperature drying. At the same time, because the material dried in vacuum atmosphere is free of oxidation, the physical, chemical and biological properties of the dried products can be completely unchanged. The application of vacuum freeze drying is expanding year by year. The specific application is shown in the table below.
The original color, aroma, taste, shape and nutrition of the product, especially the drying of heat sensitive materials, is a promising drying method for the production of green food.
|Application scope||Application example|
|Biological Preservation||Plasma, bacteria, arteries, bones, skin’, cornea, nerve tissue|
|Precious or Thermosensitive Drug Production||Enzymes, vaccines, hormones, antibiotics|
|Food Production and Preservation||Coffee, seafood, fruit, condiments|
|Micropowder drying||Amino acid, metal powder, mineral powder|
|Model||Pump Model||Pumping Speed||Ultimate Vacuum||Inlet Diam||Motor Power (Kw)|
|Main Pump||Fore Pump||Main Pump||Fore Pump|
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