Freeze-dried foods have been dehydrated in a vacuum. During the process, the food freezes and must be heated to facilitate dehydration. Explain both how the vacuum speeds up dehydration and why the food freezes as a result.
In the drying process of food, the pressure is controlled by using partial vacuum. The vacuum increases the sublimation. It makes a drying process convenient.
Moreover, water vapor solidify on the surface of the cold condenser chamber, therefore as a result, food freezes.