(1) Pretreatment of Freeze Dry gf-machine
General pretreatment refers to all treatments before sublimation drying, so freezing before drying is also a pretreatment. Raw material pretreatment is the same as conventional fruit and vegetable drying and quick-freezing of fruits and vegetables. If it needs to be selected, cleaned, peeled, cut, blanched, cooled, etc., please refer to the relevant contents of this book for details. When the juice or vegetable juice is lyophilized, it is first concentrated by a relatively inexpensive processing method, and then the product is granulated during pre-freezing.
Pre-freezing is to freeze the pre-treated raw materials for the freezing process and equipment), which is an important process for lyophilization. Since a series of complex biochemical and physicochemical changes occur in the freezing process of fruits and vegetables, the quality of the freeze-dried fruits and vegetables will be directly affected by the quality of the pre-freezing. The key consideration in the freezing process is the effect of the freezing rate of the frozen material on its quality and drying time. There are the following differences between quick freezing and slow freezing: ice crystals produced by quick freezing are smaller, ice crystals produced by slow freezing are larger; large ice crystals are good for sublimation, small ice crystals are not good for sublimation; small ice crystals have less influence on cells, and ice crystals are smaller.
(2) Sublimation drying of Freeze Dry Machine
It is the core process in the production of freeze-dried food. To control the process conditions:
①Loading capacity:When drying, the wet weight loading of the lyophilizer, that is, the quality of the drying on the drying plate per unit area, is an important factor in determining the drying time. The thickness of the food to be dried is also a factor affecting the drying time.
In lyophilization, the drying of the material is carried out from the outer layer to the inner layer. Therefore, when the material to be dried is thick, a long drying time is required. In the actual drying, the dried material is cut into a uniform thickness of 15 to 30 mm. The amount of material to be loaded on the drying plate per unit area shall be determined according to the heating method and the type of dry food. When using industrial large-scale equipment for drying, if the drying cycle is 6 ~ 8h, the dry plate material loading is 5 ~ 15kg / m2.
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It is the core process in the production of freeze-dried food to control the process conditions:
②Drying temperature In freeze-drying, in order to shorten the drying time, it is necessary to efficiently supply the heat required for sublimation of ice crystals, and thus various practical heating methods have been designed. The drying temperature must be controlled within a range that does not cause the ice crystals to melt in the material to be dried, and the dried portion does not cause heat denaturation due to overheating. Therefore, in the single heating mode, the temperature of the drying plate should be controlled at 70 to 80 ° C in the initial stage of sublimation drying, 60 ° C in the middle of drying, and 40 to 50 ° C in the late drying stage.
③Dry end point judgment Dry end point can be judged by the following indications: the material temperature and the heating plate temperature are basically consistent and maintained for a period of time; the pump set (or cold trap) vacuum gauge and the drying chamber vacuum gauge tend to be consistent and maintain a section Time; the drying chamber vacuum gauge cold trap temperature basically returns to the indicator when the equipment is empty and keeps for a period of time; for the freeze dryer with large butterfly valve, the large butterfly valve can be closed, and the vacuum machine basically does not drop or drop very little. The above four judgments can be used alone or in combination or in combination.
(3)Post processing of Freeze Dry Machine
Post-processing includes unloading, semi-finished product sorting, packaging and other processes.
After freeze-drying the knot speed, inject nitrogen or dry air into the drying chamber to break the vacuum, and then immediately remove the material in a closed environment with a relative humidity of 50% or less, a temperature of 22 to 25 ° C, and less dust, and in the same environment. The selection and packaging of semi-finished products. Because the lyophilized material has a large surface area and is very hygroscopic, it is necessary to complete the operations in a relatively dry environment.
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