How does freeze-drying work?
Freeze drying (also known as Lyophilization) is a dehydration process typically used to preserve a perishable material, or to 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 sublimate directly from the solid phase to gas. Sublimation is the action that gradually causes shrinkage of unused ice cubes in frost-free freezers and the disappearance of winter snow without thawing. The application of high vacuum in freeze drying sublimates ice much more quickly, making it useful as a deliberate drying process. A cold condenser chamber and/or condenser plates provide a surface(s) for the vapour to re-solidify on. These surfaces must be colder than the temperature of the surface of the material being dried, or the vapour will not migrate to the collector. Temperatures for this ice collection are typically below -50 C. The greatly reduced water content that results
