Process steps of plum processing
1 Raw material handling
The harvested plums are firstly subjected to “peeling” treatment to remove the waxy layer on the surface of the peel, so that the sugar can easily penetrate into the inside of the pulp.
2 Hardening and color protection
There is a tannin substance in plum pulp. During the processing, due to the oxidation of tannin substance, the product turns in gray-brown and would affect the appearance, so it is necessary to prepare a mixture of hardening and color protection. 0.1% calcium dichloride plus 0.1% sulfurous acid should be prepared for immersing the raw materials in the sodium hydrogen mixture for 8 hours, then wash it with clean water and drain the water for later use.
3 Prepare the sugar solution
50 kg of fresh fruit needs to be made into 40% sugar solution by using 25-30 kg of white sugar. Add 0.1% citric acid and 0.05% potassium sorbate to the solution. After boiling the sugar solution, put the raw materials into the solution for dipping.
4 Immersion Sugar process
After the plums were immersed in the sugar solution, the concentration of the sugar solution dropped significantly the next day. Generally, the concentration is only about 20%. It is necessary to concentrate the sugar solution and extract the light sugar solution, afterwards, heat up and concentrate the sugar solution in a jacketed pot or stainless steel pot. It is required to increase the concentration by about 5%. Add the concentrated sugar solution to the plums while it is still hot. This process should be repeated every 1-2 days. Only the sugar liquid is required to be boiled, and the raw materials cannot be directly heated. When the sugar liquid keep continuous to rise, it is the process of continuous evaporation of water in the raw material and continuous absorption of sugar. If there is no vacuum sugar immerse equipment, this process is relatively long, generally it takes 15-20 days for the sugar liquid to rise to 55-60% concentration. The sugar liquid concentration in the pulp needs to reach more than 50% before the sugar immerse is completed.
Plum drying process
Pick up the plums from the sugar liquid, lay them in the material tray, and push the material cart into the drying room. The 6P heat pump dryer is equipped with a drying room with a length of 5.8 meters and a width of 2.2 meters. 8 sets of material trucks could be pushed into the drying room. Each car is loaded with 90 kg of material, which means a total of 750kg of material could be loaded at one time. The temperature of the drying room is controlled at 60°C-70°C for 20 hours, and the moisture content is controlled at 25-28%.
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