Astronauts require preserved food for extended flights, and freeze-drying Freeze drying is a method of preserving materials. Given these facts, which of the following keeps food viable for extended flights?  among the following options:
- evaporation
 - microwaving
 - boiling
 - freeze drying
 - layers of fat
 - deep frying
 - mechanical
 - Dehydration


 

    freeze drying     