Freeze-dry (brief named Freeze-dry) is a stable process of material dried which will put the material contained with water to freeze to solid first, then make among them of the water sublimate from solid to air condition, removing water to preserve materials

Products at solution stage are frozen through sublimation and desorption, then the solvent reduce to a certain extent, thereby preventing the formation of micro-organisms or chemical reaction between the solute and solvent that products can be preserved for a long time and maintained its nature.

Vacuum freeze-drying method is a liquid → solid → gaseous process. In freeze-drying process, "liquid bridge" between the solution particles has been frozen into "solid bridge". The relative position of particles has been fixed and does not exist surface tension on gas-liquid interface between the two particles. With the continuous distillation of solvent, "solid bridge" continuously decrease, but the the relative position between two particles will not longer change until the "solid bridge" completely disappear.