Freeze-drying is a cold process that consists in freezing and dehydrating by creating a vacuum, without heat, unlike other dehydrating processes. Nutrients & flavours are retained for a long time, without the need for preservatives or additives. Considered discovered by the Peruvian Incas who were letting potatoes freeze at night and removing their water content by stomping them with their bare feet, the technology was really developed in the twentieth century as a way to preserve medicine drugs, in particular from WWII for blood plasma and penicillin, and food for astronauts. No more bare foot involved!