Commercial freeze dryer
Vacuum freeze drying is a process in which water is removed from a product after it is frozen and placed under a vacuum, allowing the ice to change directly from solid to vapor without passing through a liquid phase. Commercial freeze drying works by freezing the material, and then reducing the pressure and adding heat to allow the frozen water in the material to sublimate. Commercial freeze dryer enables people to extend the shelf life of various products from a matter of days or weeks to years or even decades.
Commercial freeze dryer is often confused with drying equipment. But the two are actually very different, both in how they are produced, and the quality and shelf life of the finished product. Processed by industrial vacuum freeze drying machine, the freeze dried fruits and vegetables typically lasts much longer and retains more of the food’s nutrient profile and taste.
There are various methods to freezing the product. Freezing can be done in a freezer, a chilled bath (shell freezer) or on a shelf in a commercial freeze dryer. Cooling the material below its triple point ensures that sublimation, rather than melting, will occur. This preserves its physical form. The freezing is done rapidly. For materials that tend to precipitate, annealing can be used. This process involves fast freezing, then raising the product temperature to allow the crystals to grow. The second phase of commercial freeze dryer is primary drying (sublimation), in which the pressure is lowered and heat is added to the material in order for the water to sublimate. The vacuum speeds sublimation. The cold condenser provides a surface for the water vapor to adhere and solidify. The condenser also protects the vacuum pump from the water vapor. About 95% of the water in the material is removed in this phase.
The final phase of commercial freeze dryer is secondary drying (adsorption), during which the water molecules are removed. By raising the temperature higher than in the primary drying phase, the bonds are broken between the material and the water molecules. Freeze dried materials retain a porous structure. After commercial freeze dryer process is complete, the vacuum can be broken with an inert gas before the material is sealed. Most materials can be dried to 1-5% residual moisture.
Commercial freeze dryer has a broad scope of application, particularly in the food and pharmaceutical industries. Freezing immobilizes the sample, thus allowing it to retain its original form; also, the absence of water prevents microbial growth and chemical changes leading to deterioration of the sample. Because water sublimates so readily, the conditions needed to freeze dry a food do not remove most other constituents.