Vacuum Drying

The vacuum drying process is to place the material in a closed drying room, and use the vacuum system to vacuuming the material while heating the material continuously, so that the moisture inside the material diffuses to the surface through the pressure difference or concentration difference, and the water molecules obtain enough on the surface of the material.

After overcoming the mutual attraction between molecules, the kinetic energy escapes to the low-pressure space of the vacuum chamber and is pumped away by the vacuum pump. Vacuum drying can easily recover useful and harmful substances, and can achieve good sealing. In the sense of environmental protection, some people call vacuum drying "green drying".

In the vacuum state, the boiling point of the material moisture is lowered and the vaporization process is accelerated, so it is especially suitable for materials that are sensitive to temperature and easily decomposed. Vacuum drying is mainly carried out in the low vacuum area.

During the vaporization process of grain moisture, its boiling evaporation temperature is proportional to the environmental pressure. The high-moisture grains are placed in a closed drying cylinder to form and maintain a certain degree of vacuum, and at the same time, the grain in the drying cylinder is continuously heated. The moisture inside the grain is diffused to the surface through the pressure difference, and after being vaporized, it is evacuated by a vacuum pump, so that the high-moisture grain can be continuously dehydrated and dried under a vacuum and low temperature state.

Vacuum drying reduces the boiling evaporation temperature of water from 100 °C to below 40 °C. Since the evaporation temperature is lower than the gelatinization temperature of starch, it will not cause damage to the grain. It avoids the swelling and bursting of the grains, and can ensure the quality of the dried grains. It ensures that the original color, aroma, taste, nutritional content and quality of the material remain basically unchanged after drying.

The vacuum freeze drying technology is to freeze the material first, and then heat it up under vacuum conditions, so that the ice sublimates to achieve the purpose of final drying. The heating methods used include infrared heating, microwave heating, etc. The heat provided should not only quickly sublimate the ice, but also not damage the surface of the product. Vacuum freeze-drying technology can maintain the original color, aroma, taste, shape and nutritional components of the product, especially for the drying of heat-sensitive materials, it is a promising drying method for the production of green food.


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