Drying of red jujube by drying technology

The processing of red jujube has two methods: natural drying and artificial drying:

Natural drying: due to the long time and many uncertain factors, it needs a large number of manual flip, dried product color is also uneven, not suitable for large-scale operation.

Artificial drying: there are many methods, more traditional is suitable for coal combustion heat for drying. In the past two years, air pollution has been serious, environmental protection departments have been heavily supervised, and coal fired boilers have been banned in many places. At the same time, coal combustion process will produce a large number of sulfides, food processing will also produce secondary pollution. After that, drying with coal is no longer the best choice. The following mainly introduces the application of dryer in drying red jujube.

Drying is the core of red jujube processing. The drying of red jujube is the process of moisture evaporation and sugar transformation under the premise of preserving the original quality of red jujube as much as possible. Red jujube contains abundant sugar, which contains polysaccharide is a kind of substance without sweet taste, must be transformed into monosaccharide under the action of biological enzyme, this is the reason why the red jujube becomes sweet after ripening. We need to make the sugar in red jujube fully transformed under the action of biological enzymes, we need to enhance the activity of biological enzymes. Through long-term practice, we have found the optimum temperature of sugar conversion of red jujube at about 60 degrees.

1.Temperature rise stage

During the drying process, if the red jujube fruit directly enters the high temperature environment suitable for sugar transformation, the huge geothermal difference causes the red jujube to have the biological protection reaction, the epidermal cell hole shrinks, the crust hardens, prevents the red jujube internal water evaporation. Therefore, in the early drying period of red jujube need to be fully preheated, gradually heating, for a large amount of water evaporation preparation .45 ℃ to maintain 2 hours, when the red jujube temperature of 45 ℃, a little hot hand, waiting for 2- 3 hours, when the red jujube body will be forced to wrinkle; When the temperature of red jujube reaches 45 ~ 48 ℃, a layer of water droplets will appear on the surface of red jujube.

2.Drying stage

When the free water in red jujube was evaporated, the temperature must be raised to 65 ℃ in the drying room within 3-5 hours, but not more than 70 ℃. In order to keep the indoor temperature constant, the moisture should be evaporated in large quantities and dehumidified. When the surface of red jujube fruit wrinkles, dry normal.

3.Dehumidification stage

When the internal temperature of red jujube is uniform, this stage can be completed within 6 hours. Because the red jujube moisture is not much, we should pay special attention to temperature control, do not oversize, 50 ℃ is the best. At this time the relative humidity also fell down, such as above 60 cents can be slightly dehumidified. As the moisture in the red jujube gradually balanced, it also reached the purpose of drying. Take care to unload the dry samples in time.

4.Cool off

Dried red jujube must pay attention to ventilation and heat dissipation, wait for cooling before piling up. If the jujube, which had just been unloaded from the oven, was stacked in the storehouse, because the red jujube itself contained so much sugar, the sugar would easily ferment and deteriorate under the action of heat, and the raw pectin in the red jujube would also be decomposed into pectin and pectin acid, which would inevitably make the red jujube a mud stall. Also can make the red jujube sugar change, appear with sour silk, so that the red jujube is destroyed. Therefore, after drying, must be thoroughly cooled before it can be stored.