Lyophilisation, usually called freeze drying, is the process of the removal of water from a product due to volatilization and desorption. The aim of the process is to achieve the comparative and reduction of other quality aspects.
Field of Application
The technique is used for drying coffee extracts, herbs, soup vegetables, flowers, ready meals, fish, meat, etc.
Techniques, methods and installation
This process is carried out in a lyophilization plant that consists of:
- a drying chamber with temperature-controlled boards (this can be a batch chamber where the trays remain fixed on the heating plates during the drying process, or semi-continuous types where the trays go through a vacuum lock in a drying tunnel);
- a capacitor to collect the water that comes out of the product in the drying chamber
- a cooling system to guide coolant to the shelves and the capacitor
- a vacuum system to reduce the pressure in the room
- a capacitor to facilitate the drying process.
If the incoming product is a liquid (eg coffee extract), the liquid is frozen in two steps (each with its own freezing temperatures and times) and ground. The solid material is then placed in the drying chamber in the drying chamber. The temperature of the drying chamber is far below 0 ° C. The exact temperature depends on the product that is being dried. A vacuum is applied in the room. The ice evaporates under these conditions. This evaporation causes a further lowering of the temperature of the product which is compensated by adding heat (by means of heating plates) to the product through the temperature-controlled trays. The evaporated water is again frozen on the surface of a capacitor that has a temperature far below the sublimation temperature below the existing properties in the chamber. From time to time the capacitor is freed by heating the surface of the capacitor. The water is liquefied and drained. The vacuum is maintained by a vacuum pump. The outlet of the vacuum pump is expelled into the air. To prevent solids from entering and damaging the vacuum pump, a filter is usually placed in front of the pump.