Freeze drying is the process of putting food into a deep freeze at -40F or colder. Once the food is frozen,  the machine then turns on heaters (slightly heating the food) and a vacuum pump, creating a powerful vacuum seal. This extracts all moisture, during this process the machine remains in a deep freeze instantaneously turning the moisture into a gas, maintaining the structure of the food and keeping the nutritional value.  Freeze dried food is processed between 24 - 50 hours, it is then sealed in oxygen, moisture proof bags, along with an oxygen absorber. You are now left with a product that if stored properly can last up to 25 years.