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Freeze drying of food offers several advantages over many other food preservation methods. There are three steps involved in the freeze drying process, but only one step to preparing a freeze dried meal. Just add water.

Lets look at the advantages of freeze drying over other food preparation methods. This will explain why freeze dried food is particularly well-suited for long term food storage programs.

Foods that are frozen retain their fresh flavor and nutritional content, but they also require constant, low temperature storage conditions, and most importantly electrical power. Canned and dehydrated foods are shelf-stable, but the high temperatures used in manufacturing can alter the flavor, texture and nutritional value of the food. Freeze drying comprises the best of these other processing methods. Freshness, aroma, and color are similar to frozen food, while also providing the shelf stability of dehydrated and canned food.

The freeze drying process of different foods varies with temperature, time, pressure, and other intermediate steps. Foods are first tested for bacterial counts. Next, the food may be cut into smaller pieces, depending on its original size. For example, thick meats do not freeze dry very well, so they must be cut into smaller chunks before freeze drying.

Some foods such as meat and seafood are cooked before freeze drying. Many fruits and vegetables are simply washed first. Others, like peas and corn, must be blanched first.

The food is flash frozen next by placing it on trays, the trays placed on carts, and the carts rolled into cold rooms where the temperature reaches as low as -40 F.

Next, the carts are moved from the cold room into the vacuum drying chamber. The drying stage involves a process known as sublimation. Sublimation is where a solid material is forced to change state into a gaseous state without ever becoming a liquid. The process is started by removing the air with a vacuum pump. The temperature is then raised to about 100 F.

The pressure in the vacuum drying chamber is now below the triple point. The triple point is where water can simultaneously exist as a solid, liquid, and gas. Next, the heat causes the ice crystals to change into a water vapor, which is then drawn off leaving only the food behind.

At this point, the dried food is filled with tiny voids, similar to a sponge. These voids are where the ice crystals were once present. This makes the food easier to absorb water when it is prepared for eating.

The dried food is then tested for moisture content and purity. Some foods may be ground into small pieces or even into a powder. Different ingredients are then blended together and the resulting food is packaged in airtight containers to prevent them from absorbing moisture from the air.

In the end, freeze-dried foods have several advantages over other types of foods used in long term food storage. Freeze dried foods retain all the fresh taste and nutritional content of frozen foods. Also, unlike dehydrated foods which shrink and shrivel under the high temperature drying process, freeze dried foods maintain their original shape and texture. They also weigh less than fresh food and take much less storage space. As long as they are kept in their original packaging, these foods stay fresh longer and can be stored at room temperatures.