Vacuum drying process is to be dry material placed in airtight dry indoor, using vacuum pump system of vacuum and heating the material to be dry, make the material internal moisture diffusion by pressure difference or a concentration difference to the surface, the kinetic energy of water molecules on the surface of material gain enough, after the mutual attraction between the molecules, escape to the vacuum chamber of low voltage space, which is the process of vacuum pumping away.Vacuum drying can be easily recycled useful and harmful substances, and can achieve good sealing.From the sense of environmental protection, has called for “green” dry vacuum drying.
In the condition of vacuum, the boiling point of material moisture reduced, evaporation process accelerated, therefore is especially suitable for sensitive to temperature and decomposition of the material.Vacuum drying is mainly in low vacuum in the region.Grain moisture content in the process of evaporation, the boiling evaporation temperature is proportional to the environmental pressure, the high moisture food placed in airtight drying cylinder, make drying cylinder form and maintain a certain degree of vacuum, within the drying cylinder on food heating at the same time, make the food the internal moisture diffusion to the surface by pressure difference, after vaporization is vacuum pump away, realize the continuous vacuum low temperature condition of high moisture food dehydration.Vacuum drying to reduce water boiling evaporation temperature from 100 ℃ to 40 ℃ below, due to the evaporation temperature is lower than the starch gelatinization temperature, not on the food grain damage.To avoid the expansion of the food grain and waist, can guarantee the product quality after drying of food.To ensure the material after drying the original color, aroma, taste, nutrition, quality basically remain unchanged, is a real sense of low temperature drying, totally different from the general hot air temperature drying.
Vacuum freeze drying (vacuumfreezedrying) technology is to make the material first to freeze, and then under the condition of vacuum, dry ice sublimation to reach the final purpose.By way of heating have infrared heating, microwave heating, etc., provided by the heat to quickly make ice sublimation, and can’t make the product surface damage.Vacuum freeze drying technology can keep use vacuum atmosphere in the recent 20 years in the food preservation of the rapid development of packaging technology.Because this kind of packing not only has exempted from oxygen make food not easy to rot, stick put oneself and inflatable packaging can be not affected by insects damage and inhibit the growth of mold, can improve and extend the characteristics of food preservation and storage time, and most packaging equipment has simple structure, convenient operation, low price, the plastic packaging materials of low cost, beautiful and easy, easy to popularize.More kinds of food vacuum packaging, such as pickle, turnips, kelp, sausage, reasonable, roast duck, bean products, milk powder, hose, etc.Due to fresh product from harvest to the other by the intermediate links in the process of time longer, loss serious easy to improve the sales price, and promotion of vacuum packing process, will make fresh cold storage fees and prices of the products is reduced, which can mitigate the spear cycle between supply and demand.So the roots vacuum pump will certainly become a great market potential and active in people’s life.
Vacuum freeze drying technology first appeared in the early twentieth century, developing rapidly in recent years.This is because it and usually thermal drying, hot air drying, the infrared drying, high frequency drying compared with many advantages.Because of the freeze drying process is to be dry material frozen, and then pumping air into vacuum state, make the material has been freeze into ice water without liquid and sublimate directly removed.So after freeze-dried products, not only can show porous state and keep its original shape, then its easy restorable after adding water, and the thermal decomposition can also prevent drying at low temperature.Materials due to dry vacuum atmosphere from oxidation, so after drying of products, its physical, chemical and biological properties can be completely the same.The application range of the vacuum freeze drying is expanded year by year.Specific application shown in the following table.
Products of the original color, aroma, taste, shape, and nutrition, especially for drying of thermal sensitive material, is the production of green food a drying method is promising.