The main advantage and distinctive feature of freeze dehydration is that the process takes place at subzero temperatures. The dried product is pre-frozen, and moisture removal occurs due to sublimation – phase transition from solid to vapor state, bypassing the liquid state. The ice-vapor phase transition can be realized under certain conditions in accordance with the phase diagram for water. The partial pressure of water vapor and the temperature of the material must be below the corresponding values for the triple point. Due to the low-temperature conditions of freeze dehydration, the original properties of the product are not only preserved (volatile? biologically active substances, original odor, taste, color), but also improved due to the concentration of the most valuable components.

Freeze drying proceeds in three main stages: pre-freezing of the product; removal of all frozen moisture from the product by sublimation (period of constant drying rate); removal of part of the unfrozen (bound) moisture with increasing temperature to an acceptable level (period of falling drying rate). In freeze drying of pharmaceuticals, the freeze drying stage is the key stage in the formation of internal structure and morphology of particles, solubility and stability of the dry product. In addition, loss of biological activity of pharmaceutical substances is possible at this stage. The process of freeze drying of products of microbiological, food, medical and other industries takes place mainly in conditions of medium discharge at temperatures from -5 to -35 °С. The lyophilic drying unit consists of a drying chamber, a desublimator condenser and a vacuum pumping system.