Freeze-Drying Made Simple:

Place the item to be dried (let's say a slab of beef) between several hollow plates filled with refrigerant. Both the beef and the plates are surrounded by an enclosing box from which the air can rapidly be removed via vacuum pump when needed. Currently the interior of the box is at normal atmospheric pressure. The refrigerant in the plates will cause ice crystals to form from the moisture in the meat exactly as a freezer would.

The air is then rapidly evacuated from the chamber via the vaccum pump and the refrigerant in the plates replaced with a warm gas causing the ice crystals in the meat to sublimate, drying it out in the process. To put it another way, the combined temperature and low pressure causes the water in the ice crystals to boil off. Picture it as freezer burn applied to the whole slab of meat rather than just one section of it.

Some examples of possible dehydrated food items include grape and orange drinks, cinnamon toasted bread cubes, fruit cocktail, chocolate cubes, turkey bites, applesauce, cream of chicken soup, shrimp cocktail, beef stew, chicken and rice, turkey and gravy, and even ice-cream.

Freeze drying allows for a significant reduction of food weight and volume, increased shelf-life, and flavours and textures closely resembling that of the original fresh food items (though this is debatable).