A freeze dryer is a low-temperature dehydration process that removes water from a material by freezing it and then lowering the pressure, allowing the frozen water in the material to change directly to a vapor (sublimate) . Freeze drying is also known as lyophilization or cryodesiccation. The process maintains nearly all of the nutritional value of fresh food, unlike other methods of preservation such as canning and dehydrating, which use high temperatures.
Freeze dryers work in three phases: freezing, primary drying (sublimation), and secondary drying (adsorption) . During the freezing phase, the material is cooled below its triple point to ensure that sublimation, rather than melting, will occur. This preserves the materials physical form. Freeze dryers use various methods to freeze a product, including a freezer, a chilled bath (shell freezer), or on a shelf in the freeze dryer.
The primary drying phase is the most critical phase, and it involves removing the majority of the water from the material by sublimation. The secondary drying phase involves removing the remaining water molecules that are adsorbed to the material. Proper freeze drying can reduce drying times by 30% .
Home freeze dryers are available for purchase, but consumer choices for this appliance are currently limited. Laboratory and commercial freeze dryers typically have more sophisticated software programs that significantly increase the price. Freeze dryers work best in ambient temperatures of 45°F to 80°F, and the pump throws out heat, so it is important to put the machine in an area where there is plenty of ventilation. When the vacuum pump turns on, the noise level is 62 to 67 decibels.
