There are various drying methods, such as sun drying, boiling drying, drying, spray drying and vacuum drying, but common drying methods are usually carried out at temperatures above 0 ℃ or higher. The products obtained from drying generally have problems of volume reduction and texture hardening. Most of the volatile components are lost, and some heat sensitive substances undergo denaturation and deactivation. Some substances even undergo oxidation. Therefore, there is a significant difference in the characteristics of the dried product compared to before drying. The freeze-drying method is basically carried out below 0 ℃, that is, in the frozen state of the product, and the analytical drying generally does not exceed 60 ℃. Under vacuum conditions, when water vapor sublimates directly, the drug remains in the frozen ice shelf, forming a sponge like porous structure. Therefore, its volume size remains almost unchanged after drying. Before reuse, simply add injection water and it will dissolve immediately.

Compared to conventional methods, freeze-drying machines have the following advantages:

1. Many thermosensitive substances do not undergo denaturation or inactivation.

2. When dried at low temperatures, the loss of some volatile components in the substance is minimal.

3. During the freeze-drying process, the growth of microorganisms and the action of enzymes cannot be carried out, so the original characteristics can be maintained.

4. Due to drying in a frozen state, the volume remains almost unchanged, maintaining the original structure and preventing concentration.

5. Due to the presence of water in the material in the form of ice crystals after pre freezing, inorganic salts dissolved in water are evenly distributed throughout the material. During sublimation, dissolved substances in water precipitate, avoiding the phenomenon of surface hardening caused by inorganic salts carried by the migration of internal moisture to the surface in general drying methods.

6. After drying, the substance is loose and porous, appearing sponge like. It dissolves quickly and quickly after adding water, almost immediately restoring its original shape.

7. Due to the drying process being carried out under vacuum with very little oxygen, some easily oxidizable substances are protected.

8. Drying can remove over 95% to 99% of moisture, allowing the dried product to be stored for a long time without deterioration.

9. Due to the frozen state of the material and the low temperature, the temperature requirement for the heating source is not high. A heater at room temperature or low temperature can be used to meet the requirements. If the freezer and dryer are separated, the dryer does not need to be insulated and there will not be a lot of heat loss, so the utilization of thermal energy is very economical.