Humidity gradient and temperature gradient are the internal power of drying Lycium chinense. When the Lycium chinense is dry, the surface water evaporates over the equilibrium water, and the internal water diffuses from the inside to the outside. The greater the humidity gradient and temperature gradient, the faster the water diffusion. When both internal and external water content of Lycium chinense reached equilibrium water content, water diffusion stopped. During the drying process, the water diffusion in the fruit was slower than that on the surface, which affected the drying rate. Therefore, reasonable control of drying factors to speed up the internal moisture diffusion, thus accelerating drying. However, if the temperature of the medium was changed, the surface of the Lycium chinense would evaporate too fast and harden, but the drying rate would be delayed. In addition, because of the difference of water content inside and outside the Lycium chinense, the internal stress will be produced very early, and the cracking of the Lycium chinense surface will be caused when the stress is serious.
In the drying process, the drying speed determines the quality of Lycium chinense. The drying speed is related to the drying method, and is affected by heating mode, heating temperature and medium temperature, humidity, airflow speed, fruit varieties, state and other factors.
The following important problems should be paid attention to during drying of Lycium chinense:
1.It is not suitable to pick. After flowering, Lycium chinense gradually develops into green young fruit, then fruit develops into orange fruit, and then gradually becomes bright red. The best time for picking is when the fruit pedicle is loose and the pulp is slightly soft. If harvested too early, Lycium barbarum will turn into wampee after drying, which will affect its quality and grade.
2. It is not suitable to remove moisture. Lycium chinense should not be picked in the morning when there is dew or when the rain is not dry. If the wet fruit is picked, the fruit surface will not dry for a long time, and will be easily contaminated by bacteria. The dried fruit will be dark in color.
3. Not to be bruised. Pick and put lightly, and use basins, barrels, baskets, baskets and other containers to prevent crushing or collision during handling. As a result of bruises, crushes, bruises, falls, stabs, etc., after drying will become black.
4.It is not suitable to expose to the sun. After sunrise, the fruit can be dried. First, there is weak light and low temperature gradually to strong light and high temperature, so that the fruit is bright red. If the fruit is exposed to the sun at hot noon, it is easy to blacken.
5.It should not be prolonged. The Lycium chinense picked should be aired or dried in time, but should not be kept for a long time. Because fresh-picked Lycium chinenses breathe strongly, and are prone to fever and sweating, they are stored for too long, and the fruit after sun-drying is not bright and gray.
6.It should not be turned over. Lycium chinense in the process of drying, after turning the meat injured, after drying, it will become black. Therefore, the Lycium chinense should not be turned in the middle after drying, and can not be collected until drying.
7. It is not suitable to fumigate. Lycium chinense fruit should not be fumigated with sulphur, although the fruit color is fresh after fumigation with sulphur, it is easy to be polluted.
8.It should not be mixed up. When Lycium chinense fruit is dried, it is necessary to take advantage of the drying process to pick out the fruit pedicels, fruit handles, black spots, wampee, shaped fruits and other impurities and pack them in graded packages, and store them in a ventilated and dry place in order to prevent moths, turning over and mildew.
The automatic Lycium chinense processing production line includes the following systems: (1) automatic cleaning/sorting system; (2) automatic feeding system; (3) automatic loading system; (4) automatic drying system; (5) automatic unloading system
Using hot air medium produced by high temperature heat pump, heating and drying can be realized by circulating fan feeding into oven and contacting fresh fruit. For the tunnel drying system with continuous production, Dryfree's experience shows that the material can be dried thoroughly if the inlet air temperature is controlled at 55-60 C, the return air temperature is controlled at 40-45 C, the humidity of the inlet air is controlled at 35-45%, the wind speed is controlled at 0.20m/s-0.35m/s and the drying time is controlled at 30 hours. This method has the advantages of low drying cost, large processing capacity, easy operation, automation and stable quality.
The popularization and construction of lycium chinense drying system with high temperature heat pump is of great significance: (1) It can liberate farmers from the complex and high-tech drying production of Lycium chinense, and devote themselves to the production of Lycium chinense planting, thus ensuring farmers'income and improving their enthusiasm for planting. (2) It is conducive to the large-scale development of high-quality Lycium chinense, brand Lycium chinense, and the formation of scale and brand advantages. (3) It is conducive to mobilizing multi-resources investment, comprehensively improving the level of Lycium chinense industry, developing modern Lycium chinense economy, enhancing competitiveness, and increasing local income; (4) it is conducive to the formation of professional cooperatives, and to the development of large-scale.