Freeze drying is a complex food preservation technique. First, the product is exposed to a deep freeze of -40°C. While maintaining this temperature, the product is then exposed to a deep vacuum for several days. This converts all the water in the product from ice directly into a vapour in a process called sublimation. Overall, 99.9% of the water is removed from the final product, allowing it to be stable at room temperature for up to 25 years while maintaining 97% of the original nutritional value.