Freeze-drying is a dehydration process especially suited to the conservation of biological products.The fundamental principle in freeze-drying is sublimation, the shift from a solid directly into a gas.
Just like evaporation, sublimation occurs when a molecule gains enough energy to break free from the molecules around it.
The direct transition of water from solid to vapor, without a liquid phase, helps to preserve most of the initial raw material’s properties such as appearance, shape, taste, color, and flavor.
As an important functional property, the freeze-dried product has a high rehydration capacity. The main limit to the industrial development is its cost due to the low productivity.
Consequently, except the application for biological active material (bacteria, vaccine), the use of freeze-drying is restricted in food industry to high added-value products like coffee,
ingredients for ready-to-eat foods (fruits and vegetables, meat and fish), and aromatic herbs.
Freeze drying has been particularly successful for coffee extracts, when its use for other foodstuff liquids/solids has markedly declined in the last decades.