Question

how are freeze dried foods prepared

Answer 1

The freeze drying process is applied in order to preserve and store foods without the need for refrigeration. Freeze drying food uses a process called lyophilization to lower the temperature of the product to below freezing, and then a high-pressure vacuum is applied to extract the water in the form of vapour. The vapour collects on a condenser, turns back to ice and is removed. Finally, a gradual temperature rise extracts all remaining 'bound' moisture from the product. This process retains the physical structure of the food product and preserves it for re-hydration at a later date. With freeze drying, foods and liquids can be dried at low temperatures without damaging their physical structure. Freeze-dried foods don’t need to be refrigerated or preserved with chemicals and can be reconstituted quickly and easily by adding water.

Sources
https://www.madehow.com/Volume-2/Freeze-Dried-Food.html (How freeze-dried food is made - material, used, processing, structure, procedure, steps, product)