How to Dehydrate Food Under a Vacuum

By Sara Tomm

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.

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Dehydrated food

Step 1

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.

Step 2

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.

Step 3

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.

Step 4

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."

Step 5

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.

Step 6

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.