It is the process by which water (and other solvents) are removed from a frozen material by sublimation and processes: freezing, primary drying (sublimation), and secondary drying (desorption)
Accelerated Freeze drying (also known as lyophilization) is a dehydration process typically used to preserve a perishable material or make the material more convenient for transport. Freeze-drying works by freezing the material and then reducing the surrounding pressure to allow the frozen water in the material to sublime directly from the solid phase to the gas phase.
The three major steps in a freeze drying include freezing, primary drying(sublimation), and secondary drying (desorption). Each step is critical in producing the required quality end.