What is freeze drying of coffee?
Freeze drying takes place from a frozen product under vacuum below the “triple point” = 4.6 torr (6.2 mbar). Below the triple point water will only be present in two phases: ice and vapour. By adding energy to the ice, it will sublimate directly into the vapour phase without passing the liquid water phase. Due to the high total solids in the coffee concentrate it is, however, necessary to operate at a much lower pressure (higher vacuum) than at the “triple point’. The low pressure (high vacuum) prevailing in the freeze drying chamber/cabinet means that the water vapour has an enormous volume. (1 l water on vapour form at 0.4 mbar = 2800 m3). To maintain the vacuum the vapours are therefore condensed as ice on the surface of tubular cooling/condensing vapour traps. The vapour traps are placed inside the freeze drying chamber. One vapor trap is in operating while the other is automatically separated from the tunnel and de-iced. Prior to the actual freeze drying process the concentrated c
