Freeze dryers need to pay attention to these in the field of food freeze-drying, but don't ignore them.

Freeze dryers need to pay attention to these in the field of food freeze-drying, but don't ignore them.
With the continuous development of China's economy, food industry, freeze dryer technology, the demand for freeze-dried food in the international and domestic markets, people have further understanding of the characteristics of convenient, health care, nutrition, sanitation and storage resistance. It has also spurred the increasing number of food freeze-drying processing enterprises. However, the application of freeze dryer in the field of food processing also needs to pay attention to the following factors:
Note 1: Pre-cooling rate and pre-cooling end temperature.
1 Pre-cooling rate optimization The freezing process will produce ice crystals of different particle sizes and directly affect the sublimation drying speed. The results of the study express the relationship between the freezing rate and the shape and number of ice crystals, which are mostly block, strip and piece. The fruit and vegetable raw materials are degraded under the traditional slow freeze-drying process, and the foods prepared under the vacuum freeze-drying process can basically maintain the original quality, and the practice shows that the proper freezing method A pre-freezing pre-freezing rate does not affect the quality of the product, but also accelerates the drying rate.
2 Pre-freezing end temperature optimization During the sublimation drying, the material has some liquid, which will evaporate rapidly under vacuum, causing liquid concentration, loss of nutrients and shrinking product volume. Therefore, the pre-freezing end temperature is generally required to be lower than the material eutectic point temperature (the temperature at which all moisture in the food material is frozen, which can be determined by the electric resistance method, and the pre-freezing end temperature can avoid the freezing temperature being too low or too high, resulting in excessive freezing energy consumption or Affect the quality of the product, generally lower than the material eutectic point temperature of 5 ° C -10 ° C or so.
Note 2: heating method and temperature. Most food lyophilization adopts radiant heating method. In this way, the tray containing the material is placed in the middle of the two radiant heating plates, and the heat is transferred to the material by the upper and lower heating plates (separators) in the form of radiation, and the heating temperature ( The temperature of the separator must be maintained in the water sublimation stage to maintain the material ice layer not exceeding the point of incorporation (completely frozen food, when the temperature rises to a certain point, the temperature point at which ice crystals begin to melt, can be determined by the electric resistance method as the high limit of Zui, Otherwise, it will seriously affect the quality and appearance of the freeze-drying process and freeze-dried food. Therefore, under the specific heat transfer mode, the sublimation and desorption process of the drying process can only be shortened under the premise of ensuring the quality of the product by using reasonable heating temperature. Drying time increases drying efficiency and thus reduces energy consumption.