Drying is the process of drying products using heat and air. Heat will cause the water in the product to evaporate, while air will carry the moisture out of the drying chamber.

Freeze drying is a process of drying a product by removing water through sublimation. Sublimation is the process in which a substance changes directly from a solid to a gas state without passing through the liquid state.

Within the limits of the article, we will not present overly academic but only explain in an easy-to-understand and imaginative way for all customers.

The process of water sublimation

To explain more clearly the above definition, Haitan presents the process of water evaporation as follows.

The chart above shows 3 states of water: solid phase, liquid phase and gas phase. The intersection point of the 3 state lines is called the Triple Point.

If the pressure is higher than the pressure of the Triple Point. When heated, water will change from solid to liquid, and then vaporize. This is a process that we often see under atmospheric pressure conditions.
If the pressure is lower than the pressure of the Triple Point. When heated, water will change from solid to sublimated directly.

The Triple Point of water is O(0.0098°C; 4.58 mmHg).

Therefore, the vaporization process of water occurs when the environmental pressure is reduced below the Triple Point pressure. At low temperatures, water is in a solid state. As the temperature rises, water will gradually vaporize into the gas state.

Components of a freeze dryer

A freeze dryer consists of many components, but we will analyze the following three parts:

• Vacuum pump: This device creates a vacuum environment for the drying process.
• Freezing unit: This device helps to freeze the product at the beginning of the drying process. It also absorbs moisture released from the product during drying.
• Heating unit: Once the product is frozen and the vacuum pump has created a sufficient vacuum, the heating element heats the product to initiate the sublimation process.

The drying process works like this:

The freeze drying process 3 main stages.

Initial stage:

The freezing unit will freeze the product. Typically takes 6-8 hours. In some production lines, to save time, the product will be pre-frozen in a quick freezing machine. Then, it will be put into the drying chamber.

Drying stage:

The vacuum pump removes all the air inside the drying chamber, creating a vacuum environment. The electric resistor will heat up to melt the ice into water vapor.

The water vapor evaporates and escapes outside the product will be reabsorbed in a part called the water trap. The temperature in the water trap is usually lower than the temperature in the drying chamber by about 20°C. When the water vapor enters the water trap, it will immediately condense back into ice.

Final stage:

At this stage, only moisture vapor remains deep inside the product. At this point, the electric resistor will heat up very high, up to 70°C. The process continues until no more moisture vapor escapes outside.

Some related questions

Is freeze drying the same as drying at low temperatures?

During the sublimation process, the temperature in the drying chamber will always be at a negative temperature. In fact, in the water trap, the negative temperature is very deep.

However, there will be a heating element design on the product tray. In order for the sublimation process to take place, the product can be heated up to 700C.

With a very complex drying technology such as freeze drying, it is difficult to conclude simply whether the drying temperature is negative or not.

The product is heated up to 700C, so are the nutrients and vitamins destroyed?
In fact, it is not at all. Dry nutrients and vitamins are destroyed at very high temperatures, possibly over 1500C.

The reason why the product changes in nature, color, and smell during drying is usually due to strong oxidation when heated above 400C. However, in the freeze-drying chamber, oxygen and air have been removed, so oxidation no longer occurs.

WHERE TO BUY A FREEZE DRYER?
With the initiative in freeze-drying technology, Haitan Dryer has launched freeze-drying machines with versions: mini, pilot and industrial with modern, industrial designs. Suitable for scales from households to industrial

Haitan Dryer is a unit specializing in manufacturing and distributing all types of food and agricultural product dryers. In the past year, Haitan Dryer has distributed more than 100 sublimation dryers to users nationwide.

So through the article “What is freeze drying?” Haitan has partly helped you understand more about the principle of freeze drying, the water freeze process as well as the structure of the freeze dryer. You can learn more about some models at the link below

See types of freeze Dryers HERE

For detailed advice and quotes on freeze dryers, please contact Hotline+91 9266 325252, we are ready to answer all of your questions.