There are many possible reasons for the black color of yam. It may be that the yam was not soaked in water in time during processing, causing the surface to be exposed to the air. After contact with oxygen in the air, an "enzyme-mediated oxidation reaction" formed, causing the surface to turn black. It may be that rusty knives were used during the cutting process of the yams, or they were corroded by bacteria during storage, resulting in black spots on the surface. If soy sauce and other pigment-containing seasonings are added to the yam when stewing it, it will also turn black.

If the yam turns black, you can take the following measures to solve it. Before cooking, it is best to soak the yam in water for about 20 minutes to dissolve the starch and alkaline substances in it. Clean knives should be used when cutting, and the surface of the yams can be coated with cooking oil or vinegar after cutting to prevent exposure to air. To avoid moisture and contamination during storage, it is best to keep it in a dry, ventilated, and cool place.

There are many reasons why yams turn black when cooked, and we need to pay attention to details during the cooking process to avoid this situation. Some treatments can be done to yams before cooking to ensure their quality and taste. If we have found black spots on the surface of the yam, we can solve it by applying oil or vinegar. When eating, pay attention to check whether there are dark spots or signs of deterioration on the surface of yams to ensure food safety.