The basic principle of freeze drying is based on the three-state change of water. Water has solid, liquid and gaseous states, and the three states can both be converted to each other and coexist. When water is at the triple point (temperature is 0.01 °C, water vapor pressure is 610.5Pa), water, ice and water vapor can coexist and balance each other. In the high vacuum state, the principle of sublimation is used to make the water in the pre-frozen material be removed directly into water vapor in the ice state without melting the ice, so as to achieve the purpose of freeze drying. Freeze-dried products are sponge-like, no shrinkage, excellent rehydration, very little moisture, and can be stored and transported at room temperature for a long time after corresponding packaging. Because vacuum freeze drying has unparalleled advantages of other drying methods, this technology has been more and more favored since its inception, and its applications in medicine, biological products and food have become more and more extensive. Serum, strains, traditional Chinese and Western medicine and other biological products are mostly bioactive substances, and vacuum freeze drying technology also provides a good solution for preserving biological activity.
