Notes on manual drying of fruits and vegetables

1 temperature rise

Manual drying requires that in a relatively short period of time, the use of appropriate temperature, through ventilation and dehumidification operation management, to obtain high quality products. In order to achieve this goal, the key is to use different heating methods for different kinds of fruits and vegetables. Generally, it can be divided into the following three types:

(1) During the drying process, the temperature of the drying room is low at the beginning, high at the middle, low at the end. This heating method is suitable for fruits and vegetables with high content of soluble substances, and is widely used at present.

(2) During the whole drying period, the temperature of the drying room rises sharply at the initial stage, up to 95-100 ℃. After the raw materials enter the drying room, they absorb a lot of heat and lower the temperature of the drying room, which is generally reduced by 25-30 ℃. At this time, continue to increase the firepower to raise the temperature of the drying room to 70 ℃ for a period of time, and then gradually lower the temperature until the end of drying depending on the drying state of the product. It is suitable for fruits and vegetables with low soluble matter content, or fruits and vegetables cut into thin slices and filaments, such as daylily, pepper, apple, apricot, etc. Using this heating method to dry fruits and vegetables, the drying time is short, and the product quality is good. However, the technology is difficult to master, the coal consumption is high, and the production cost increases accordingly.

(3) The heating mode between the two above means that the temperature is maintained at a constant level of 55-60 ℃ during the whole drying period, and then gradually decreases until the end of drying. This heating method is suitable for the drying of most fruits and vegetables, the technology is easy to master, and the product quality is poor.

2 ventilation and dehumidification

When the fruits and vegetables are dried, a large amount of water evaporates, which makes the relative humidity in the drying room rise sharply, and even reach the degree of saturation. Therefore, it is necessary to strengthen the ventilation and moisture removal in the drying room. Generally, when the relative temperature in the drying room reaches more than 70%, ventilation and dehumidification are needed.

3. Change the drying plate

Even if the drying room is well designed and reasonably constructed, the temperature difference between the upper part and the lower part, the front part and the rear part should be more than 2 ~ 4 ℃. Therefore, the raw materials in the drying pan near the main fire channel and furnace are easier to dry than those in other parts, especially in the middle of the drying room, and even Coke will occur. In order to make the drying degree of the finished product consistent and avoid the uneven state of drying and wetting as far as possible, the drying plate must be changed.

4. Master the drying time

Dried fruits and vegetables should be baked until the finished product reaches its standard moisture content, and then enter the process of softening, grading, packaging and storage. When to finish drying depends on the degree of drying required for the product.