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Freeze-drying Process of Vacuum Freeze Dryer

The vacuum freeze dryer is suitable for the drying of high-end raw materials, Chinese herbal medicine, biological, wild vegetables, dehydrated vegetables, food, fruits, chemicals, pharmaceutical intermediates and other materials. The freezing vacuum drying process is that no impurities are mixed into the object, which can keep the original ingredients and active ingredients of the material and the shape of the material intact. Compared with the traditional high-temperature drying process, the freeze-dried product processing process generally includes the following steps: pre-processing, pre-freezing, quick freezing, sublimation and analysis.
 
I. Pre-processing
The source and application of raw materials are different, and their pre-processing methods are also different. For example, the pre-processing of fruits is selection, washing and cutting, while vegetables need to be blanched, and instant porridge needs to be steamed and plated.
 
II. Pre-freezing
The raw materials generally need to be pre-frozen first after they are pre-processed. This is because when the material has a lot of water inside, if the vacuum treatment is directly carried out, the gas dissolved in the water will escape due to the reduction of external pressure and forms into bubbles, resulting in cavities inside and on the surface of the raw material so that it will affect the sensory quality.
 
III. Quick freezing
In order to solidify the moisture inside the material, quick freezing is usually required. The shorter the freezing time, the faster the material freezes, and the smaller the internal crystallization, the less mechanical damage to the material cells. Therefore, it is necessary to select an appropriate freezing speed according to actual production.
 
IV. Vacuum drying
Vacuum drying is generally divided into two stages: sublimation drying and analytical drying. Sublimation drying is mainly aimed at free water in materials, while analytical drying is mainly to remove adsorbed water that is strongly combined with solids. The degree of vacuum, temperature and plate thickness during the drying process directly affect the drying process and product quality.

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