The core of date palm fruit processing is drying, it is the process of internal moisture evaporation and sugar conversion under the premise of preserving the original quality of the date palm as much as possible. Date palm is rich in sugar, and the polysaccharide contained in it is a non-sweet substance that must be converted into monosaccharide under the action of biological enzymes to become sweet. This is why dates palm become sweeter when ripe. Practice has proved that increasing the temperature within a certain temperature range can improve the biological activity of the enzyme. At the same time, sugar is a highly heat-sensitive substance and has a certain coking temperature, so the drying temperature of dates palm must be lower than the critical temperature of sugar coking.
During the dates fruit drying process, if the dates fruit directly enters a high temperature environment suitable for sugar conversion, the huge temperature difference will cause the jujube fruit to undergo a biological protection reaction, and the stomata of the epidermal cells will shrink, crust and harden, thereby preventing the evaporation of the water inside the jujube fruit. When the temperature of the jujube fruit reaches 40 ℃, it can only enter a suitable temperature environment by gently pinching it. After entering this temperature zone, a lot of water evaporates, the sugar in the date palm is converted under the action of biological enzymes, and the taste becomes sweet. In the later stage of drying of dates, the free water inside and outside the dates has evaporated a lot, and the evaporation rate has decreased. The effect of temperature on the evaporation of water inside the dates fruit decreases, while the humidity difference between the inside and outside of the dates fruit increases, and the internal water naturally permeates and evaporates to the outside. At this stage, the temperature in the drying room should be lowered to reduce the effect of temperature on the evaporation of water in the dates fruit, so that the humidity difference between the inside and outside of the dates fruit should be kept within a reasonable range, so that the internal and external evaporation of the dates fruit can be balanced. The slow evaporation of water in red dates and balanced evaporation inside and outside are the factors to maintain the fruit shape of dates.
Date Palm drying machine is a special equipment for drying dates and date slices. The equipment greatly improves labor efficiency and product quality. Improper selection can lead to low efficiency, high energy consumption, high operating costs, poor product quality, or even failure of the device to operate properly. Therefore, the ideal selection must be determined according to its own use conditions. Pay attention to the following when using the date palm dryer:
1. Classify the dates fruit according to the variety, size and maturity to make the dryness consistent. Then, the pallet loading capacity of dates fruit is about 20-30 kg per square meter, start the dates fruit dryer.
2. Preheating: During the dates fruit drying process, if the date palm directly enters a high temperature environment suitable for sugar conversion, the huge temperature difference will cause the biological protection reaction of the date palm, the pores of the epidermal cells will shrink, and the hard shell will become hard, preventing the inner part of the date palm. Water evaporates. Therefore, it is necessary to fully preheat the date palm in the early stage of drying, and gradually increase the temperature to prepare for the evaporation of a large amount of water. Hold at 35°C for 6-10 hours. When the temperature of the jujube reaches 45℃, it feels a little hot. After 7-8 hours, when the dates are pressed hard, wrinkles will appear. When the temperature of the jujube reaches 45-48 ℃, a layer of small water droplets will appear on the dates.
3. Evaporation: The free water in the dates fruit is greatly evaporated. At this time, the temperature must be increased, and the temperature of the drying room should reach 65 °C within 8-12 hours, and should not exceed 70 °C, so as to facilitate the evaporation of water. Pay attention to dehumidification, keep the indoor temperature changing little, and make the water evaporate continuously. When wrinkles appear on the surface of the date palm, it means that the drying is normal.
4. Drying: When the temperature in the dates fruit is uniform, this stage of work can be completed within 6 hours. Because there is not much water in the later stage of the date palm, special attention should be paid to temperature control, not too high, 50 ℃ is better. The relative humidity also drops at this time, and if it is higher than 60%, it can be drained slightly. With the gradual balance of moisture in the dates fruit, the purpose of drying is achieved.
5. Cooling: The roasted dates must be ventilated and cooled before stacking. If the dates just unloaded from the drying room are stacked in the warehouse, due to the high sugar content of the dates, the sugar is easily fermented and deteriorated under the action of heat, and the original pectin in the dates will also decompose into pectin and pectin. The acid turns the date palm into a puddle of mud, changes the sugar content in the date palm, and causes the date palm to be destroyed by the acid silk. Therefore, after drying, it must be thoroughly cooled before storage.