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In the past, dried fruits often used the hot drying method, but this method was not too effective in keeping the nutrients in the food intact. And so, when the freeze-drying method was born, it was more popular.
So what exactly is the freeze-drying method? What principle does the food freezer work? Let’s find out with lassho.edu.vn right away.
What is freeze drying?
Freeze drying is a drying method using dry air, with a humidity of about 10 – 30%, at a temperature lower than 35 – 60 degrees Celsius compared to normal drying temperature. Freeze drying can be understood as being carried out under atmospheric pressure.
Because the temperature when freeze-dried is quite low, so the food when freeze-dried has almost little effect on the quality and still retains the nutrients .
Food freeze drying method
Working principle of refrigerator
Freeze drying is carried out in a refrigeration dryer (also called a heat pump). Refrigeration dryer has a structure consisting of 1 heat pump (placed in a drying cabinet or drying tunnel), a heat pump with 2 heads: 1 hot end and 1 cold end .
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The hot end will be responsible for providing heat for drying.
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The cold head is responsible for dehumidifying the drying air.
Freeze dryer
The specific operating principle of the refrigerator will take place as follows:
Air with high humidity (in the drying chamber) will be drawn into the condenser coil’s tube. Here, the air will be cooled so that the water vapor can be separated , becoming dry and cold air .
Next, this airflow will be led through a hot chamber with a temperature of 35 – 60 degrees Celsius. The air continues to be led into the drying chamber containing the food to freeze the food.
This process will be repeated continuously , the cold dry air after drying will become hot and humid air. This process takes place continuously to freeze the food.
Working principle of refrigerator
The difference between cold drying and hot drying
The same two methods of drying food, but between cold drying and hot drying, there are the following differences:
| Cold-drying | Heated | |
| Working principle | Use dry air to dry | Use heat to dry, the higher the heat, the faster the steam in the food will escape |
| Structure | The dryer is bulky, large and has many parts | Simple and compact structure |
| Drying temperature | 35 – 60 degrees C | 40 – 100 degrees Celsius or higher, depending on the type of food |
| Food characteristics when finished drying | Optimal color and nutrition retention | Keep the color and nutrition but not as good as freeze drying |
| Type of dried food | Often drying high-grade foods | Often drying common foods |
| Dryer price | 2-3 times more expensive than dryer | Cheaper |
The difference between freeze-dried and hot-dried food
Here’s everything you need to know about freeze drying. Hope this information will help you in making healthy food choices.
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