Soak yam in clear water in time after cutting. Water can isolate air and delay the oxidation process of yam. You can also add a proper amount of vinegar to the water. Acetic acid can inhibit the oxidation process of ferrous ions, and water can isolate air. The combination of the two is better.
Yam contains ferrous ions. When yam is cut, ferrous ions are exposed to the air and react with oxygen to generate iron oxide, which is reddish brown in color and turns dark brown when it is highly oxidized. Therefore, yam will not be oxidized as long as it does not touch the air. The cut yam can be placed in the solution and isolated from the air.