Freeze drying or lyophilisation is a procedure for the gentle drying of high-quality products. The product is dried by sublimation without passing through the liquid phase.

As far as their sheer quantity is concerned, foodstuffs are the major application for freeze drying. One widely known example is the production of granulated instant coffee or the drying of fruit, e.g. for breakfast cereals. Other areas of application are the restoration of water-damaged documents or the drying of archaeological artefacts. 

Another important area of application is the drying of biotechnological and pharmaceutical products, e.g. tissues and tissue extracts, bacteria, vaccines, and sera. Products that would not keep well when they are dissolved in water can be preserved by freeze drying. During this process, the biological properties of these sensitive substances are preserved. The compounds remain unchanged from a qualitative and quantitative point of view. After the addition of water, the products will have the same characteristics as the original products.