Take raw yam, remove moldy or spoiled yam and impurities, and wash thoroughly. Cut into 3-4mm thick slices, place in a stainless steel steaming container, and soak in a color-protecting solution at a ratio of 1:1.5 for 3 hours. Remove from heat, place in a yam dryer, and dry at 60°C until the moisture content of the yam slices does not exceed 9.0%. Remove from heat, cool, sieve to remove debris, and package.

Processing precautions:

1. After washing the raw yam, slice it quickly to prevent oxidative browning caused by polyphenol oxidase. After soaking, dry the yam slices in the air, otherwise the drying time of the sulfur-free yam slices will be affected.

2. To meet the actual needs of large-scale production, the drying temperature should be set within a certain range. Based on actual temperature measurements of the yam dryer, the drying temperature is set between 55-65°C.

3. Soak the yam in color-protecting liquid at a ratio of 1 to 1.5 for 3 hours. The production method of sulfur-free yam: the composition of the color-protecting liquid is 1.5% citric acid, 2.5% sodium chloride, and 0.5% calcium chloride.