Summary of key technology characteristics and application of microwave drying equipment for jujube

- May 06, 2019 -

Industrial microwave equipment has gradually attracted people's attention in production and application. Microwave equipment brings energy-saving, high efficiency, low-carbon, environmental protection and good benefit production technology to our industrial production. More manufacturers of dried and sliced jujube began to choose microwave drying equipment. However, how can microwave drying equipment be used more efficiently? How to make your jujube have the best drying quality? This article will show you several key factors in the drying process of jujube. The magnetic field distribution in the microwave oven is not uniform. In order to ensure the uniform heating of materials, the placement of jujube must be careful. We put the jujube on the tray in the microwave heating box (which can make the multi-layer tray). When heating, the jujube rotates with the tray at a uniform speed, so that the material can receive the microwave radiation in the box evenly. The temperature and humidity of the material in the box can be controlled in time by the intelligent temperature control and humidity control system outside the box. The temperature and moisture content of jujube in the first 60 seconds did not change significantly when the jujube was dried in microwave equipment during the drying process, because it was a preheating period. At 60s-90s, the temperature of jujube rises rapidly, which is due to the strong penetration of microwave and the rapid heating of the whole object from outside to inside. After 90 s, the heating rate of jujube slowed down. When the surface temperature of jujube reached 70 C, the microwave source stopped releasing energy. When the surface temperature drops to about 30 C, then microwave heating is applied. At this time, the water content of the central part of jujube is very low, which leads to the decrease of the microwave absorption ability of jujube. However, there are a small amount of oil extracts in the interior and core of jujube, which will continue to heat up under microwave irradiation at high temperature and generate thermal radiation. At this time, if the thermal radiation of chemical components in jujube is neglected, microwave radiation will continue to be released. When drying jujube, special attention should be paid to material temperature control. Rate of one-sided pursuit of rate and water evaporation efficiency should not be allowed, and the phenomenon of burning caused by too fast rise of central temperature should be prevented. Therefore, the time of microwave irradiation was controlled within 190s, and the surface temperature of jujube was controlled below 70 C. The drying quality of jujube was the best. The moisture content of

4 and

materials is an important quality index, which directly relates to the suitability of the taste of the materials, the brightness of the materials, and the storage time. Considering the shelf life and storage difficulty, it is generally believed that the lower the moisture content of dried jujube, the better. However, it was found that dry jujube with moisture content of about 21% had the best taste and effect.

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