Food Freeze Dry Machine—Freeze-Drying Process I


1.Operation points (1) Pretreatment of Freeze Dry Machi […]

1.Operation points

(1) Pretreatment of Freeze Dry 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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