Abstract: Freeze drying apparatus in which a liquid product is sprayed into a freezing chamber to produce a frozen powder, which drops on to a multiple stage conveyor in a drying chamber under vacuum. The drying chamber is open to the freezing chamber and is also maintained at freezing temperature. The moisture content of the frozen powder is sublimated by microwave radiation, which does not heat the chamber or the conveyors and causes minimal temperature increase of the powder. The dry powder is carried on a further conveyor, through a microwave excluding choke, to a collection chamber. Cold water vapor is constantly removed from the drying chamber by the vacuum pump and condensed in a heat exchanger, from which the resultant ice is removed by microwave radiation to minimize temperature variations in the system.