"Reverse steaming", also known as "three steaming and three drying", is a special production method of dried sweet potatoes. Reverse steaming means that the sweet potatoes steamed once or twice are exposed to the sun and then returned to the steamer to continue steaming. Why do you want to use this production method? Isn't it troublesome to do so? Dried sweet potatoes made by the ancient method of reverse steaming are sweet and chewy, Q-elastic, not sticky, and the more you chew, the more fragrant it becomes. After eating it, you will know that although this processing method is tedious and time-consuming, it is really worthwhile. The "three steaming and three drying" of dried sweet potatoes all have different purposes, one steaming is ripe, the other steaming is sweet and the third steaming is soft. Therefore, three steaming and three drying are indispensable. The process of making dried sweet potatoes by "three steaming and three drying" is quite complicated, and it is made by spreading moisture, washing, cooking, slicing, drying in the sun, steaming again, drying again, steaming again and drying again. Because it is cooked and dried in the sun, and then steamed twice, it is named "backward steaming ancient method", which is also listed as a national intangible cultural heritage.