Reasons For Pre-freezing Of Fruit And Vegetable Freeze Dryers

The pre-freezing time of the fruit and vegetable freeze dryer is generally controlled at 2h to 4h. According to the thickness, characteristics and pre-freezing temperature, the material containing a large amount of water is frozen into a solid. It forms crystals that are more conducive to sublimation, and may form a glass state when frozen. After drying for a period of time, an upper drying layer and a lower freezing layer are formed. When the freezing layer continues to dry, the sublimation airflow must pass through the drying layer. Continued drying will be affected to a large extent. effect, resulting in drying failure.

To ensure that all products obtain the same microstructure, all products are usually frozen to a certain low temperature during freeze-drying, and the entering temperature is usually 5 °C for a period of time to prevent uneven structure and color. To avoid bubbling during sublimation under vacuum, the pre-freezing temperature must be lower than the eutectic temperature of 5°C.