Freeze drying or lyophilization is a low temperature dehydration method, famous for drying products without lose their biological activity. Freeze drying also is considered to be one of the best ways to dry products, this is due to its unique working principle: Sublimation technology.
The fundamental principle in freeze drying is sublimation: a water remove process based on freezing the raw material to solid phase, reduce frozen product surround pressure enable the water boiling point reduce, solid ice will direct sublimate to vapor. By this, the water in product success removed.
Freeze Drying Working Steps
Raw product thoroughly freezing is the guarantee of a success freeze drying. Liquid water will remain in frozen product if the freezing is incomplete, once the drying chamber goes to negative pressure in vacuum stage (water boiling point will reduce), the liquid water remained will start boiling and destroying product structure.
Frozen product placed in drying chamber, vacuum environment created and the sublimation starts. About 95% physical water removed.
The water remaining after primary drying is bound water. More energy is needed to remove the bound water, along with a higher vacuum degree.