Firstly, the material to be freeze-dried is frozen at sub-zero temperatures, thus maintaining its molecular structure. The frozen material is inserted into the freeze drier, where there is a vacuum pressure, due to the action of a vacuum pump that allows it to function properly. This pump allows 95% of the water present in the sample to be sublimated, and in this way, the product dries without the need to use temperatures above the ambient temperature.
The heat contained in the lyophilizer provides the necessary energy to the water to pass to the gaseous state, accelerating the process. And the gas that's left loose, is condensed at low temperatures, returning back to solid state.