Freeze drying (or lyophilization) is a technique used to remove water from a solution to leave a dry ‘cake’ as an end product. The dry product is much more stable than a solution. The reduced weight and volume is a big advantage and the removal of the water does not change the activity of the product. This technique involves freezing the product on a shelf to very low temperatures, typically –40 to –50°C, applying a vacuum and then slowly heating the product to initiate the ice to turn into vapor and this removes the water content from product by a process called sublimation.
The critical parameters during freeze-drying are temperature (product and shelf) and pressure. These measurements are usually recorded with every cycle to determine when the product is dry. In addition to monitoring each cycle, freeze driers also require regular validation. This will generally involve temperature mapping of the shelves in the chamber as well as validation of steam supplies for SIP system.
As freeze drying is a rather expensive process most products being processed are within the pharmaceutical and biotechnology area where companies often use freeze-drying to increase the shelf life of products, such as vaccines and other injectables. By removing the water from the material and sealing the material in a vial, the material can be easily stored, shipped, and later reconstituted to its original form for injection.
You can still find lyophilization performed in other areas :
Food industry (example: freeze dried fruits, astronaut food supplies, instant coffee).