The difference between freeze drying and ordinary drying

2021-02-01 10:50:19
The difference between freeze drying and ordinary drying
The refrigeration system of the freeze dryer is an important part. Theoretically, the refrigeration system is composed of a refrigeration compressor, a condenser, an evaporator and a thermal expansion valve. It is mainly used to provide cold energy for the pre-freezing of the products in the drying box; and for the later stage The cold trap coil captures the sublimation water vapor to supply cold energy.

The design of the freeze dryer takes into account the particularity of refrigeration requirements. Its refrigeration system is mainly composed of compressors, refrigerants, oil separators, water condensers, filter driers, intercoolers, sight glasses, solenoid valves, hand valves, Expansion valve, evaporator, vapor-liquid separator, gas filter, pressure gauge, pressure control relay, energy regulator, safety valve, refrigeration pipeline, etc.

freeze drying technology (freeze drying for short) is a new type of food processing technology, which is very healthy and harmless to the human body. Let’s take a look at how it differs from ordinary drying:

Ordinary drying is one of the methods to keep the material from deteriorating. There are many drying methods, such as sun drying, boiling, drying, spray drying and vacuum drying. However, these drying methods are all performed at temperatures above 0°C or higher. The product obtained by drying is generally reduced in volume and hardened in texture. Some substances have been oxidized, and most of the volatile components will be lost. Microorganisms will lose their biological vitality, and the dried substances will not easily dissolve in water.

The principle of freeze drying is well understood. First, put fresh fruits and vegetables into a freeze dryer at minus 50°C for freezing. After the fruits and vegetables are frozen, vacuum the drying box and increase the temperature slightly after the vacuum is formed. The ice in the fruits and vegetables is directly sublimated into water vapor and separated from the fruits and vegetables, while the “skeleton” of the fruits and vegetables remains unchanged in volume and loose and porous. The moisture that can be removed by freeze drying can reach more than 95%.

freeze drying technology is carried out at low temperature, such as protein, microorganisms, etc. will not be denatured or lose biological activity. When drying at low temperature, the loss of some volatile components in the substance is small, which is suitable for drying some chemical products, medicines and food.

During the freeze drying process, the growth of microorganisms and the action of enzymes cannot proceed, so the original properties can be maintained. Since the drying is carried out in a frozen state, the volume is almost unchanged and the original structure is maintained without concentration. Since drying is carried out under vacuum, there is very little oxygen, so some easily oxidized substances are protected. Drying can remove more than 95-99% of water, so that the dried product can be stored for a long time without deterioration.