Freeze drying: Basic theory & applications

Freeze drying is the most gentle process to dry various types of perishable materials. The principle of freeze drying is based on the direct transition of a substance from the solid to the gaseous state, called sublimation. Initially, the product is frozen and then dried by sublimation in an environment of reduced pressure. The low pressure enables direct changeover of the frozen solvent into vapor. In most freeze drying applications, the solvent to be removed from the product is water. However, other solvents can be used to a certain extent, such as ethanol.