Common dehydration and drying methods used by dehydrated vegetable manufacturers

When dehydrated vegetables are processed in dehydrated vegetable manufacturers, they will be dried first. The most commonly used drying methods are as follows:

1) Microwave drying: Microwave drying refers to the use of electromagnetic waves (microwaves) to penetrate the dried food, so that the polar molecules (water, sugar, salt) in the food rotate at a very high frequency as the polarity of the microwave changes, generating friction heat, so that the inside and outside of the dried food are heated up at the same time, and the water is quickly released to achieve the purpose of drying.

2) Normal pressure drying: The normal pressure drying process includes two stages: constant speed drying and deceleration drying. In the constant speed drying stage, the rate of water diffusion inside the meat block must be greater than or equal to the surface evaporation rate. At this time, the evaporation of water is carried out on the surface of the meat block. The evaporation rate is controlled by the diffusion rate of steam through the surrounding air film, and the drying speed depends on the temperature difference between the surrounding hot air and the meat block. When the diffusion rate of water in the meat block can no longer keep the surface water saturated, the water diffusion rate becomes the controlling factor of the drying speed. At this time, the temperature of the meat rises, the surface begins to harden, and the drying enters the deceleration drying stage. The stage when the water movement begins to feel a little difficult is the first deceleration drying stage, and the movement of most of the water in the future becomes the second deceleration drying stage.

3) Decompression drying: The food is placed in a vacuum environment. Depending on the vacuum degree, at the appropriate temperature, the water contained in it will evaporate or sublimate. There are two types of decompression drying of meat products: vacuum drying and freeze sublimation drying.

1. Freeze sublimation drying: Usually the meat is rapidly frozen to -30 to -40°C, placed in a drying chamber that can maintain a vacuum pressure of 13 to 133 Pa, and dehydrated and dried by ice sublimation. The sublimation rate of ice depends on the vacuum pressure of the drying chamber and the heat required for sublimation. In addition, it is related to the size and thickness of the meat. Although the freeze sublimation drying method requires heating, it does not require high temperature. It only needs to supply latent heat of sublimation and shorten the drying time.

2. Vacuum drying: refers to the drying of meat blocks by evaporation of water in a vacuum state (decompression) that does not reach the freezing temperature. In vacuum drying, in the early stage of drying, there is internal diffusion and surface evaporation of water, just like in normal pressure drying. However, in the whole drying process, it is mainly internal diffusion and internal evaporation that occur together. Therefore, compared with normal pressure drying, the drying time is shortened and the surface hardening phenomenon is reduced.