Freeze drying method
The freeze drying method is a process to quick freeze internal water of material, then removing the water directly from ice to vapor by sublimation. According to freeze drying method, we got to know that the freeze drying machine must be equipped with the ability to quick freeze, we have to note that it is quick freeze rather than simply freeze, because the quick freeze would request much lower temperature that can make the internal water of material quickly freeze into small ice crystal, and quick freeze can prevent forming big ice crystal which would destroy the internal structure, leading to less ideal quality of finished freeze dried products. Freeze dryer must also be equipped with vacuumizing function, the lower the pressure is, the lower the ice sublimation temperature is. Freeze drying machine also asked for heating function, because ice sublimation needs to absorb heating, moderate heating can speed up the sublimation.
Freeze drying method is over qualified to meet food level sanitary requirement. As freeze drying method, water is removed from materials by sublimating from ice to vapor step by step, at the same time; vapor is caught by vapor condenser congealing on the coil pipe. The fresh material is totally dry after removing all the water. Some companies make the defrosting happen by electrical heating simultaneously with the above process, which would slower the speed of catching water and fall short of saving time, while increasing the energy consumption, so it is not widely used.
When using freeze drying method, product temperature and pre-set temperature is the same, meanwhile vacuum level reached unloaded ultimate vacuum, all these conditions represent products is already freeze dried. Now you can shut down freeze dryer and release pressure, then unload freeze dried fruits and pack them promptly. The freeze dried fruit would not lose any nutrients except water, and freeze dried fruits is fluffy and porous and there is no change in size and shape. After freeze drying, the freeze dried fruits is more sweeter, more fragrant and more crispier. With the improvement of living standard, this natural and healthy freeze dried fruit crisp will be more and more welcomed by consumers. It is an ideal investing project for the short-season and high nutrient fruits.