Freeze-drying or sublimation is a process of flash freezing with the subsequent placement of the product into a vacuum environment. Thereby all the moisture is vaporized, avoiding the liquid phase, and going straight into a gas phase.
This technology was discovered in late 1906 by A. d`Arsoval and F. Bordas, French researchers at Collège de France. But it started to get widely used only in 1970s, thus many think sublimation quite new, though it is not so.
People often confuse freeze-drying with dehydration, the difference between them can be seen in the tables on the right.
During the freeze-drying products are not being put through any heat processing. Under high temperatures and duration of drying, the product is losing its nutritional values and taste qualities. Process of dehydration takes place directly at positive temperatures, ranging from 0°С to 60°С, depending on the product. And freeze-drying starts to act under low temperatures from -1°С to 70°С.
The video below perfectly describes freeze-drying process in an easy and explanatory way.
Dried products have lost most of their nutritional values, will never be recovered and will quickly deteriorate.
Freeze-dried products keep their nutritions and vitamins, and can be kept of up to 25 years.