Plum drying can be done by traditional drying or artificial drying. In traditional drying, it is done on a field in the sun, the fresh fruits are spread on meshes to dry. This method has the advantages of low cost and a large amount of drying at one time, but as a disadvantage it has difficult temperature control, irregular drying, long drying time, and poor product quality.
Instead, TROCKNNER heat pump drying is a modern and popular drying method with high efficiency and energy saving. The fresh plum is placed on a tray and goes into a drying room. The drying process includes three stages: accelerated drying, constant speed drying, and reduced speed drying.
- The first phase is the accelerated drying stage. The temperature in the chamber rises to 35 – 40 °C. When the speed of the circulating air is about 1.3 m/s, the transfer of hot air, diffusion and evaporation of free water in the plum are accelerated, especially the loss of water in the peel and it reaches 50%. , the epidermis is wrinkled, and the structural water in the plum slowly seeps and evaporates from the pores in the rind.
- The second stage is the constant rate drying stage. The plum has enough unbound water accumulated in the rind due to extravasation of water in the fruit. When the water loss rate in plum reaches nearly 50%, the indoor temperature will naturally rise to 50-55°C, and the circulating wind speed can be reduced a little. The less water there is in the plum, the shorter the dehydration time. A large amount of dehydration reduces the size to what is generally said to be in a semi-dry state. During this period, the water content is around 30%.
- The third stage is the slow drying stage. When the water content of plum drops to a certain value (about 30%), the thermal conductivity in the fruit decreases and the temperature difference between the inside and the outside increases. Due to the decrease of the water content in the plum, the evaporation rate of the water from the fruit decreases, so it takes a long time for discharge.
In short, after entering the product into the drying room, keep the temperature at 35-40°C for 2-3 hours; Heating at 40-45°C for 8 hours, then increase to 50-55°C for 8 hours, a total of 18-20 hours. This method is a gentle drying method, close to natural drying, which contributes to maintaining the quality and color of the plum.
Precautions for drying: The plum should not be wet, nor should it be stored for a long time. It is recommended to wash with a 0.5% NaOH aqueous solution and then at the time of drying, the diffusion rate of internal moisture is increased and, therefore, the drying efficiency is significantly improved.
When it comes to quality, service and value, Count on TROCKNNER Drying Ovens!
