Freeze-drying was known since about 1000 BC. During this time, South Americans would place their food high on mountains, where they would freeze and dry as the water vaporized away. Commercial freeze-drying occurred around the time of World War II, when the process was used as a medical solution. Today, more than 400 foods have been commercially freeze-dried, although some of the more popular foods are coffee and ice cream (see reference 1).
Freeze-dried food supplies hikers and campers with extremely low-weight food to pack and use. This allows for longer hikes with lighter supplies. In a survival situation, many freeze-dried foods can be eaten without any prior preparation and only need added water. Having freeze-dried foods on hand is important when you do not have time to make a meal or have more important concerns to worry about, such as shelter or environmental hazards. Freeze-dried food also comes in sealed packages that resist spoilage and water, so wet conditions won't ruin your provisions.
Freeze-fried food can be used in any circumstance, whether it is an emergency or not. If you are in a survival situation, freeze-dried foods are handy; campers, hikers, backpackers and commuters all enjoy freeze-dried foods, and thus freeze-dried items are not limited to any one circumstance. Freeze-dried food is most often eaten by adding hot water to rehydrate the product, but you can usually eat freeze-dried foods plain as well. Freeze-drying is usually preferred over regular dehydration for survival foods, because the freeze-drying process preserves the flavor and texture of the food better and has a longer shelf life.
When considering freeze-dried survival foods, pay attention to preparation instructions to ensure that you get the easier-to-make foods. Survival situations often provide little free time to spare, so making sure the packages you get can be prepared quickly is beneficial. Freeze-dried meals cost more than regular dehydrated foods, so you should consider how many you want to pack for a trip based on the number of days you will be gone.
Freeze-drying is not the same as dehydration, which uses heat. However, freeze-drying is a type of dehydration. In freeze-drying, water is vaporized from the food at around or below zero degrees Celsius. Normal dehydration uses heightened heat (between 130 and 200 degrees Fahrenheit) to evaporate liquid from food.