Dehydration of food is a process that removes its liquid content. One method of food dehydration is vacuum freeze-drying, which is used to dehydrate foods that have been previously frozen. Cooked foods dehydrated under a vacuum last longer and retain their nutritional content, color, flavor and texture. Dehydrated foods are lightweight, take up a minimal amount of space and stay fresh for months or years, making them ideal for campers. Astronauts eat freeze-dried foods during space travel.
Freeze food before you begin the dehydration process. The website Freezedry.com lists the four requirements for freeze-drying. The first is that food must be in a frozen state to be freeze-dried. The process of freeze-drying requires the liquid content of food to be in the solid state (frozen) in order to initiate vaporization.
Place the frozen food in the vacuum chamber of your freeze-dryer. According to Elizabeth L. Andress, Ph.D., National Center for Home Food Preservation, the bacteria that spoil food thrive in an oxygen-containing environment. Because the vacuum chamber is devoid of oxygen, the growth of food-spoiling bacteria is slowed, thereby helping to preserve the quality of freeze-dried food.
Begin the freeze-drying process according to the manufacturer's instructions. This process, also known as lyophilization, changes the food's liquid content from a solid to a vapor. According to the University of Georgia, College of Family and Consumer Sciences, microorganisms require a moist or liquid environment in order to survive. Therefore, removing the liquid from food during the freeze-drying process also aids in retarding degradation.
Convert the frozen liquid content of the food being freeze-dried into a gaseous state (vapor) by applying pressure and heat in the vacuum chamber. Located within the vacuum chamber are condenser plates or coils that sustain a temperature lower than the item being freeze-dried. When the vaporized liquid accumulates on the condenser plates, it is converted back into a solid state as frost and is removed from the chamber. The process of changing the frozen liquid (solid ice) into a vapor and back into a solid (frost) without first returning it to the liquid state is called "sublimation."
Reduce the weight of food by 70 to 90 percent by removing its liquid content (water) during the freeze-drying process. According to the website Wild Backpacker, after freeze-drying a half pound of frozen cooked chicken weighs approximately 2 ounces. When the ice crystals that form in frozen food are removed, small pores remain in their place. The pores make the process of rehydrating freeze-dried food take five minutes in boiling water or five to 10 minutes in cold water.
Store freeze-dried food in airtight, vacuum-sealed containers to keep moisture out. To extend the life of freeze-dried foods, it is best to store them in a cool, dry area. With proper storage, your foods will retain their flavor, texture and color for several years. The United States Environmental Protection Agency: Dehydrated Fruits and Vegetables, states that freeze-drying preserves the maximum nutritional value of foods.