freeze-drying

The freeze-drying food preservation process, first developed in the 1950s, can be used on 600 different foods. It is a two-step process involving rapid freezing and subsequent dehydration (removal of moisture). Rapid freezing helps preserve the nutrients and flavor of a food.

The freeze-drying process begins when food is placed between two cold hollow plates that contain a refrigerant liquid, in a tightly sealed chamber. While the food is being fast-frozen, a high-powered pump creates a vacuum in the chamber. Then the refrigerant liquid in the hollow plates is replaced with warm gas, which converts the ice in the food directly into water vapor. This dehydration process takes 20 hours. The food must then be packaged to seal out oxygen and moisture, either of which would cause the food to decay.