Freeze drying is the most effective way to remove water from food. Freeze drying (also known as lyophilization or cryodesiccation) is a dehydration process typically used to preserve food and make it more convenient for transport and storage. Freeze drying works by freezing the food and then reducing the surrounding pressure and adding just enough heat to allow the frozen water in the food to sublime directly from the solid phase to the gas phase.

If freeze-dried food is then sealed to prevent the re-absorption of moisture, the food may be stored at room temperature without refrigeration, and be protected against spoilage for many years. Preservation is possible because the greatly reduced water content inhibits the action of microorganisms and enzymes that would normally spoil or degrade the food.

Freeze drying also causes less damage to the food than other dehydration methods that employ the use of higher temperatures. Freeze drying does not usually cause shrinkage or toughening of the material being dried. In addition, flavors, smells and nutritional value generally remain unchanged, making the process popular for preserving food.