The reason for why lemon slices turned into black after drying is the high-temperature air flows through the surface of the material to achieve the purpose of drying during the drying process. When the lemon slices are exposed to air, there will be oxidation, and this is unavoidable. In addition, the lemon contains sugars, if the drying temperature is too high, the lemon slice will be scorched, which will eventually cause the dried lemon slices to become black. Then, how to reduce the blackening of lemon slices has become a problem faced by many distributors and customers.
At present, the drying equipment on the market is mainly divided into two types: high-temperature drying and dehumidification type and closed dehumidification and drying type. The principle of high-temperature drying and dehuminification equipment is evaporate the moisture inside the materials by high-temperature air, and and exhaust the moisture of the air by dehuminification, at the same time, it enters the fresh air from the outside, so that the fresh air in the drying room will continue to enter until the end of the drying. Therefore, in the process of dehumidification and intake of fresh air, the air in the drying room is constantly exchanged with the outside air, and the amount of oxygen will not be reduced due to the oxidation of the lemon slices, which will accelerate the oxidation of the lemon slices and eventually increase the blackening of lemon slices.
The closed dehumidification and drying equipment removes moisture through dehumidification equipment. There is no need for fresh air to enter during the drying process. Which means the air that the material comes into touch with during the entire drying process is the airs remaining in the drying room, and its oxygen content is also basically be fixed, so the oxidation of lemon slices will be reduced.
Lemons need to be cleaned before drying. There are salt water cleaning method, soda cleaning or ultrasonic cleaning method and so on. The main purpose is to clean and remove pesticide residues or wax on the lemon. After removing the wax, it can accelerate the drying process of lemon slices and shorten the drying process, and then reduce the oxidation of lemon slices as a result. It is better to use manual or lemon slicer to cut the fruit into slices with about 4mm. It should be noticed that the thickness shall be even, and the thickness error should not exceed ±1mm. Place the lemon slices neatly on a ventilated tray and avoid stacking them.
It should be quickly to transfer the lemon slices to the drying room. The drying temperature is generally around 50°C. The temperature should not be too high, because the lemon itself contains sugars. If the temperature is too high, the sugars will be scorched, causing the lemon slices to become black after drying. In general, a 15p closed dehuminification dryer is required if you want to dry 1000-1250 kg of lemon slices. The drying temperature is divided into three stages, and the three different temperature settings are 43°C, 45°C, and 50°C. The maximum drying temperature of lemon slices should not exceed 60℃. Keep the drying temperature at medium and low temperature to reduce the loss of nutrients. The drying time is about 15-20 hours, depending on the ripeness of the lemon, the thickness of the slice and the drying season. Sure. (For reference only, please do not apply it without considering practical operation.)
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