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Do you know freeze drying ?

Oct 29, 2021

What is Freeze Drying?

Water (H2O) can be solid (ice), liquid (water) and gas (vapor) under different pressures and temperatures. The change from liquid to gas is called "evaporation", and the change from solid to gas is called "sublimation". Vacuum freeze-drying is to freeze the material containing a large amount of water into a solid by cooling in advance. Then the water vapor is directly sublimated from the solid under vacuum conditions, and the substance itself remains in the ice shelf when it is frozen, so its volume does not change after drying, and it becomes loose, porous, and has good rehydration performance. In a word, freeze-drying is the heat and mass transfer at low temperature and low pressure.

freeze dried method


The full name of Freeze2Drying is VacuumFreezeDrying, or freeze-drying for short, also known as Drying by Sublimation, which freezes the dried liquid material into a solid, and uses the sublimation performance of ice under low temperature and reduced pressure conditions. , A method to dehydrate the material at low temperature to achieve the purpose of drying.

Advantage of freeze drying

There are various drying methods in freeze dryers, such as sun-drying, boil-drying, drying, spray drying and vacuum drying, etc., but ordinary drying methods are usually carried out at temperatures above 0°C or higher. The dried products generally have the problems of reduced volume and hard texture. Most of the volatile components will be lost.

Some thermol-sensitive compound will be deactivated, and some compound may even be oxidized. Therefore, there is a big properties gap the dried product compared to the one before drying.

on the contrary,the freeze-drying method is basically carried out below 0°C, that is, the product is carried out in a frozen state. Only when the residual moisture content of the product is reduced in the later stage when the product is allowed to rise to a temperature above 0°C, the whole process does not exceed 40°C. In the freeze dryer under vacuum conditions, when the water vapor is directly sublimated, the medicine remains in the frozen ice shelf, forming a sponge-like loose porous structure, so its volume is almost unchanged after drying.

freeze dried fruits

The freeze dried fruit can be restored and it will dissolve in water immediately. Compared with conventional methods, freeze dryers have the following advantages:

1. Many heat-sensitive substances will not be inactivated.

2. Since drying at low temperature, the loss of some volatile components in the substance is very small.

3. During the freeze-drying process, microorganisms and the enzymes cannot proceed, so the original properties can be maintained.

4. Because it is dried in a frozen state, the volume is almost unchanged, and the original structure is maintained without concentration.

5. Since the water in the material exists in the form of ice crystals after pre-freezing, the dissolved inorganic salt substances originally dissolved in the water are evenly distributed in the material. When the product processed by the freeze dryer is sublimated, the dissolved substances dissolved in the water are precipitated, surface won’t turn hard because of the precipitation of inorganic salts carried by the water inside the material moves to the surface like it does in the general drying method.