Lyophilization process is carried out in 3 main stages;
1- Freezing the Product: It is the process of freezing the product completely at low temperature after the preliminary preparation processes and transforming it into crystal form.
2- Sublimation (Primary Drying): It is the process of creating the necessary energy for sublimation in the frozen product and performing sublimation. It is the stage in which 90-95% of the water content is removed. The primary drying step is the longest lasting step among the 3 steps that make up the process. In this step, the pressure in the device chamber is reduced and heat is applied to initiate the sublimation of the ice crystals formed in the freezing step. The pressure inside the device chamber is reduced by the vacuum pump.
3- Desorption (Secondary Drying): In the secondary or final drying phase, the residual moisture content is reduced as much as possible to make the product permanently storable. The water retained by adsorption on the inner surface of the product must be removed. To achieve this, the capillary forces of the water often have to be overcome. Therefore, the freeze drying plant must be designed to produce a high pressure stage during the secondary drying phase. While the primary purpose of primary drying is the removal of solvent from the matrix by sublimation, the primary objective of secondary drying is to reduce the moisture content of the product to levels where biological activities or chemical reactions cannot occur.
