Principle of Freeze Dried Technology

Freeze-drying (FD) is one of the important symbols of technological progress in the food industry. This technology is internationally recognized as a high-quality dry processing method that can maximize the preservation of the tissue structure and nutritional function of food raw materials.

Freeze Dried technology is a drying technology that directly removes water molecules in materials under low pressure conditions by freezing wet materials below the eutectic point temperature and using the principle of water sublimation. The water vapor sublimated from the material is captured by the water vapor condenser in the vacuum system, so as to obtain a dehydrated product with a long storage period, a stable system and complete nutritional functions.

Freeze-Drying Process

The freeze dried process can be mainly divided into the following three stages:

1. Pre-freezing stage

This stage mainly freezes a large amount of free water in the wet material into a solid state. Generally, the appropriate pre-freezing temperature is determined according to the melting point of different materials. Since the material is in a frozen state and the material system is in a stable state, there is a significant correlation between the pre-freezing rate and the type of freeze-dried material. The ice crystals formed by quick freezing are smaller and have less impact on the cell structure of the material. Conversely, the slow freezing process produces larger ice crystals, leaving behind larger pore-like structures that facilitate water sublimation. However, larger ice crystals will destroy the original structure of cells and have a certain impact on the tissue structure of materials and related biologically active substances.

2. Sublimation drying stage (first stage drying)

At this stage, the material needs to be properly heated to sublime the free water in the frozen state, and about 90% of the total water in the material is removed during this period. Different materials have differences in their own material composition, moisture content, moisture distribution and moisture state and other characteristics, resulting in differences in the heat required for moisture sublimation at this stage. In this stage, it is necessary to ensure that the temperature can not exceed the eutectic temperature of the material itself, but also exceed the sublimation temperature of water. If the sublimation temperature is too much higher than the eutectic point, the material will have volume collapse, discoloration, bubbles and other phenomena due to the reduction of water viscosity in the system. Therefore, the sublimation temperature of the material should be close to the eutectic point and exceed the water sublimation point.

3. Analysis drying stage (second stage drying):

Based on the previous stage, this stage continues to remove about 10% of the bound water that was not removed in the first stage by sublimation. This stage needs to have a high enough vacuum to ensure that the desorbed bound water has enough power to escape from the material. In addition, since the desorption of bound water requires high energy, it is necessary to ensure that the temperature at this stage reaches a certain level. Due to the different material composition, shape and residual water content of the material, the specific analysis time needs to be determined by the basic properties of the specific material.

Jintai provides a variety of fruit and vegetable products freeze-dried powder raw materials to comply with the development trend of natural, nutrition, function, health, and so on.