Pretreatment is a very important step in the operation points of the fruit and vegetable freeze dryer, so let's learn about it today:
Generally, pretreatment refers to all treatments before drying, so freezing before drying also belongs to pretreatment.
The pretreatment of raw materials is the same as that of conventional fruit and vegetable drying and fruit and vegetable quick-frozen products. If processing such as selection, cleaning, peeling, dicing, blanching, cooling, etc. is required, when the fruit juice or vegetable juice is freeze-dried, the lower price will be used first. The processing method is to pre-concentrate it and then granulate the product when it is pre-frozen.
Pre-freezing is to freeze the pre-treated raw materials, which is an important process of freeze-drying. Because fruits and vegetables undergo a series of complex biochemical and physicochemical changes during the freezing process, the quality of pre-freezing will directly affect the quality of freeze-dried fruits and vegetables.
The key consideration in the freezing process is the effect of the freezing rate of the frozen material on its quality and drying time.
The difference between quick freezing and slow freezing is as follows: the ice crystals generated by quick freezing are smaller, and the ice crystals generated by slow freezing are larger; large ice crystals are conducive to improvement, and small ice crystals are not conducive to improvement; small ice crystals have less impact on cells, and the smaller the ice crystals , the more it can reflect the original structure and function of the product after it is dry.
However, the freezing rate is high and the energy consumption required is also high. Comprehensive consideration should be given to select an appropriate freezing rate to reduce the required freezing energy consumption while ensuring the quality of freeze-dried food.