What is the Vacuum Puff Drying?

The vacuum puff process has been developed for drying liquids under vacuum. The development of processes for drying liquids under vacuum came from the observations made on the freeze drying of orange juice concentrate. The rate of drying of the product in the liquid state was double that in the frozen state (freeze drying) and the dried product had a highly porous structure, which exhibited good rehydration properties. This was due to the fact that under vacuum conditions the liquid tends to foam and produce a film structure, which dries to give a highly porous solid.