Freeze-drying means Extraction of water from frozen material. The drying process takes place by avoiding the liquid state through sublimation, i. e. direct conversion from ice to vapour. This happens under vacuum and the temperature in the product is normally less than -10°C. The aim of freeze-drying is to obtain an easily water-soluble product which will have the same characteristics as the original product after addition of water. As the drying process takes place in frozen state at very low temperatures it is possible to dry e. g. proteins which will not denature. Also most of the other chemical compounds will be qualitatively and quantitatively unchanged. Through freeze-drying, the product, mainly of biological origin - such as tissues, tissue extracts, bacteria, vaccines, and sera – is transformed into a dry product. During this process, enzymatic, bacterial and chemical changes are largely avoided.
Tasks and applications
Freeze-drying (lyophilisation) is the most gentle process for preserving the biological properties of sensitive tissue and tissue components. Lyophilisation is also the best method when drying inorganic products – e.g. nanoscale dispersions – the particle surfaces of which should remain unchanged