Principle:
i. The material is frozen in a suitable container connected to a high vacuum system, so that the vapour pressure of water is reduced to less than that of material being dried.
ii. Thus, it reduce the temperature and pressure to values bellow the triple point.
iii. Under these conditions, any heat transfer is used as latent heat and the ice sublimes directly to the vapour state.
iv. The water vapour is removed from the system by condensation in a condenser maintained at a temperature lower than a frozen material.
Advantages:
i. The product obtained is light and porous having excellent solubility.
ii. The chances of hydrolysis are minimized as drying takes place at a very low temperature.
iii. Drying takes place under vacuum; hence oxidation is minimized as there is no contact with air.
iv. The heat-sensitive materials can be dried.
v. The loss of volatile material is minimum.
vi. The freeze-dried material can be stored at room temperature if it is properly sealed in an inert atmosphere.
vii. The sterility of the product can be maintained.