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Besides hot drying, cold drying is also the best way to preserve food. Although the cost is more expensive, the quality of the product when preserved by cold drying is also much higher than that of hot drying. Today, let’s explore with Cfis.edu.vn what is freeze drying and how it works.
What is freeze drying?
Since the process is carried out under atmospheric pressure, freeze-drying is considered a method that can help product quality to be less affected by external factors by using dry air to dry food at a high temperature . The humidity is about 10 – 30% and the temperature is lower than the normal drying temperature, from 35 to 60 degrees Celsius.
Refrigeration dryers are also known as heat pump dryers, they are usually composed of a heat pump placed in a drying tunnel or drying cabinet depending on the size of the device.
In particular, the heat pump will have a hot end to help provide heat for drying food and a cold end that works to separate moisture for the drying air.
Principle of food freezing
Freeze drying is a continuous and cyclical process. Air with high humidity from the drying chamber will be drawn through the condenser coil’s duct. Here, the refrigeration dryer cools the air to condensing temperature to separate water vapor from the air and make the air a cold dry air stream.
Next, the machine will guide this cold dry air through the hot chamber to heat it to a temperature between 35 – 60 degrees Celsius . After that, to proceed to freeze the food according to the manufacturer’s wishes, the cold dry air will continue to be led into the drying chamber containing the food to be dried.
Therefore, after drying, this dry and cold air will become hot and humid air and be circulated through the trays of the food to be dried to continue the circulating drying process similar to the above process.
Distinguish between cold drying and hot drying
To distinguish between cold drying and hot drying, you can rely on some characteristics
Freeze drying is the use of dry, low-humidity air for drying. And hot drying is using heat to dry, the higher the temperature, the faster the steam escapes and helps the food to be dried faster.
About the structure
Refrigeration dryers have a rather complicated and cumbersome structure depending on their size , including a steam condensing system, a cooling system, a sub-heating unit and a blower unit.
The structure of the hot dryer is composed of an electronic control system to generate heat and uses a convection fan unit, so they are somewhat simpler and more compact.
About drying temperature
Freeze drying is carried out in the range of 35-60 degrees Celsius . And hot drying is about 40-100 degrees Celsius or depending on the type of food being dried, the temperature may be higher.
About the characteristics of dried products
Freeze-drying can help food retain its color, shape and nutrients optimally.
Hot drying will also preserve the color, shape and nutrients of the food, but the effect is certainly not as high as freezing.
About the group of dried foods
The freeze-drying method is often used for high-end items. As for common items, they will usually be dried hot.
About the price
Due to the extremely high efficiency that freeze drying brings, the cost of products when frozen will also be 2-3 times more expensive than drying.
Hopefully, through the above sharing, you already know what freeze drying is as well as the working principle of freeze drying. If you want the product to be preserved better, use the freeze-drying method!
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