The main difference between them is the water remove theory: Vacuum drying based on water boiling point, vacuum freeze drying based on water melting point.
Vacuum freeze drying also known as lyophilization or freeze drying. The drying process is by freezing raw product and then move to a drying chamber, reduce the chamber pressure, enable solid ice (inside raw product) sublimate to vapor (removed from raw product). Water removes based on sublimation (Solid to Vapor).
Vacuum drying, without freezing stage. By reduce environment pressure enable water boiling point reduce, when reach a certain range, the water start boiling and go out of raw product. So, vacuum drying water remove based on water boiling (liquid to vapor).
That also means, they will have different applications:
- Vacuum drying mainly for raw products that not very heat sensitive.
- Freeze drying mainly for areas where nutrition is need to preserve.
|Vacuum Drying||Vacuum Freeze Drying|
|Drying Temp.||+80,+60, +40||Minus|
|Dried Product Structure||Slightly Change||No Change|
|Heat sensitive product||Not suit||Yes|