Freeze dryers are a new type of refrigeration compressor air dryer developed using advanced technology and scientific research based on the traditional refrigeration air dryer production technology. The continuous development of cryogenic drying technology, the demand for freeze-dried food in the international and Chinese markets, and our further understanding of the convenience, health, nutrition, hygiene, and storage life of freeze-dried food have all contributed to the continuous increase of food freeze-drying processing enterprises. However, the application of freeze dryers in the food processing industry also needs to pay attention to the following factors:

Note 1: Pre-cooling rate and pre-cooling endpoint temperature.

① Increasing the pre-cooling rate during the freezing process will result in ice crystals of different particle sizes, which directly affects the drying rate. Research results have described the inherent relationship between the freezing rate and the shape and number of ice crystals. For most small, strip-shaped, and block-shaped fruits and vegetables, the food quality deteriorates under the traditional slow cryogenic drying process, while under vacuum cryogenic drying, the food quality can be basically maintained. Practice shows that a suitable refrigeration method and pre-freezing rate will not affect product quality and can accelerate the drying rate.

② Pre-freezing endpoint temperature optimization. During sublimation drying of freeze-dried food, some liquid remains in the material, which can quickly volatilize under vacuum, causing liquid extraction, nutrient outflow, and product shrinkage. Therefore, the pre-freezing endpoint temperature is generally required to be lower than the eutectic point temperature of the material (the temperature at which all water in the food material is frozen, which can be determined by the resistance method). The pre-freezing endpoint temperature can prevent the freezing temperature from being too low or too high, resulting in excessive refrigeration energy consumption or affecting product quality. It is generally required to be 5℃-10℃ lower than the eutectic point temperature of the material.

Note 2: Heating method and temperature.

Freeze-drying of food mostly uses radiation heating. This method places the tray containing the material between two radiation heating plates. The heat is transmitted to the material from the upper and lower heating plates (baffles) by radiation. The heating temperature (baffle temperature) must ensure that the ice surface of the material does not exceed the eutectic point during the water sublimation stage (for completely frozen food, when the temperature rises to a certain point, ice crystals begin to melt. This temperature point can be determined by the resistance method as the upper limit. Otherwise, it will seriously affect the freeze-drying process and the quality and appearance of the freeze-dried food. Therefore, under a specific heat transfer method, to improve the drying process and the sublimation process, only by using the appropriate heating temperature can the drying time be reduced and the drying efficiency increased while ensuring product quality, thereby reducing energy consumption.