Figure 7.

Schematic representation of the main stages of the freeze-drying (lyophilization) method. After the loading of the sample container (in flasks/vials), the system undergoes an initial freezing at atmospheric pressure, which is characterized by the formation of ice crystals (A), followed by a primary drying (ice crystal sublimation) (B) under vacuum. A secondary drying under vacuum favors the desorption of unfrozen water (C). Finally, the sample (product in vials) undergoes a backfill and stoppering process under partial vacuum, followed by the removal of the dried product from the freeze dryer.