Freeze drying is the process of pre cooling and freezing a substance containing a large amount of moisture into a solid, and then directly sublimating the water vapor under vacuum conditions, while the substance itself remains on the ice shelf during freezing, so the loose pore volume remains unchanged after drying. Freeze drying is carried out at low temperatures, making it particularly suitable for many thermosensitive substances such as proteins, microorganisms, etc., without causing denaturation or loss of biological activity. Therefore, it has a wide range of applications in medicine. Due to the fact that drying is carried out under vacuum with little oxygen, some easily oxidizable substances are protected. Drying can remove over 95-99% of moisture, allowing dried products to be stored for a long time without spoilage. Therefore, freeze-drying has been widely used in the pharmaceutical industry, food industry, scientific research and other sectors.
