ABSTRACT
The most important question to ask about freeze-drying is not “what is freeze-drying?” but “why do we freeze-dry?” The answer is simple: “stability.” Water is an extremely reactive compound, and many biological and pharmaceutical preparations have only limited stability in aqueous solution. Long-term storage, therefore, needs an alternative, and removing the water does seem to be a reasonable one. If a product is to be dried, then there are two readily available routes: (i) evaporation of liquid water by, e.g., vacuum drying (1) or spray drying (2), and (ii) sublimation of solid water (ice) following freezing of the solution, i.e., freeze-drying.
