Sublimation drying is the most technological production type in the industry. There are several options for marking the drying process of frozen products under vacuum:
– sublimation drying;
– freeze drying;
– molecular drying.
Despite their different names, they all represent the same process.
Sublimation is characterized by the fact that the products are dried in a frozen state. In the process of sublimation, the moisture goes into vapor from the ice state directly, excluding the liquid state. Due to these drying features, products, manufactured by the sublimation technology have a variety of characteristics and differences from products produced by other drying options:
– products fully retain the initial organoleptic properties, color, taste, structure and volume;
– due to the porous structure, products can recover in water in a few seconds;
– volatile components remain virtually unchanged;
– the shelf life of the products, produced by the sublimation drying method, reaches several years;
– in a sealed package the products may be stored under any conditions.
The essence of the sublimation drying method is as follows. First, the product, which undergone the shock-freezing stage, is placed on a pallet between the heating elements. After generating vacuum the heat from the heating elements in the installation is provided to the product in the quantity required for the ice sublimation, i.e. to transfer the water from the solid state to the vapor. he forming vapor moves from the product to the cooled surface of the capacitor, condenses and partially removed together with the incondensable gases by a vacuum pump. In order to ensure the normal flow of the process in such a system, it is necessary to retrain the pressures of the water vapor between the freeze dryer and the capacitor.
The moisture is removed from the product in three stages:
- There is a gradual pressure reduction in the chamber. The product is quickly defrosted. Ice goes to vapor state thanks to the warmth of the product itself.
- The main part of the moisture is removed directly by the sublimation.
- Residues of unfrozen moisture are removed by the thermal dryer. The characteristics of this drying type may include manual work and energy costs of the process (up to 5 kW per 1 kg of vaporized moisture).