Freeze-drying is one of the most important processes that allow freeze-drying of food products. Freeze drying is a process in which water is sublimated by directly transferring water from the solid state (ice) to vapor, thus lowering the liquid state, and then desorbing the water from the “dry” layer.
Freeze-drying or lyophilic drying takes place in three phases: freezing; primary drying (sublimation); secondary drying (adsorption). Freeze-drying is the process of removing water from perishable foods to extend their shelf life and/or prepare them for transportation. Freeze-drying is accomplished by freezing the product, then reducing pressure and adding heat to allow the frozen water to turn directly into vapor (sublimate). The first use of this technology in the food industry was to produce rations for astronauts and the military.