Introduction to Freeze Drying

1: What is Freeze Drying?

As the name implies, freeze drying describes a process whereby something is frozen and then dried. Freeze drying is also known as lyophilization (or lyophilisation) which means "solvent-loving". This name illustrates a key aspect of the process in that the products that are to be dried must be easily soluble.

Operationally, we could define the freeze-drying process as a controllable method of dehydrating labile materials by desiccation under vacuum. This may be done to achieve better stability compared to the initial formulation, or simply because the freeze-dried form is preferred by the end user.

As a stepwise process, freeze-drying typically involves:

• Cooling of the initial formulation (which may be a solution, suspension, emulsion, slurry or a more complex mixture or structure)
• Conversion of freezable solvent (usually water) into a solid
• Sublimation of the solid solvent (usually ice) under vacuum
• Desorption of bound solvent remaining in the dried product (often referred to as a "cake" or "plug")
• Sealing of the product in its container if appropriate, either under vacuum or ‘backfilled’ with a non-reactive gas such as nitrogen or argon

Freeze-drying is a unit operation that is widely used in the production of a wide range of products, including diagnostics, vaccines, pharmaceuticals, biotech products, foods and beverages.

2: Freeze Dried Products

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