6. Freeze-dryer refrigeration systems

Freeze-drying is a drying process based on the principle of sublimating the ice from a frozen product: the water in the product passes directly from the solid state to the vapor state. The water-free product thus obtained is assured of a long shelf-life, without the need for a refrigeration system.

This process is applied to pharmaceutical products, foodstuffs of all kinds, and cultural property polluted by floods, but above all it is the only process that preserves the distinctive aroma of coffee powder.

The complete operation consists of three stages, which take place inside a sealed chamber. The times quoted are average industrial values:

• freeze the product in a thin layer on trays for 1 to 3 hours, depending on its type;

• the chamber is evacuated and the...