Phenols in yam are easy to be oxidized after contact with air, resulting in colored quinones that turn purple and black. You can use the following tips:

1, completely soak the peeled fruit in clean water mixed with white vinegar.

2. Add a small amount of salt to the peeled and washed yam and stir well.

3. Put the peeled yam in a steamer for one minute, or heat it in a microwave oven for 1 minute, and then peel it.

Extended data

Raw yam is easy to turn black after peeling, which is the result of oxidation with air. It has no effect on taste, but the color is not good-looking. How can we keep yam from turning black?

It's simple. Reduce the contact time between yam and air. First, burn the yam on the fire and burn the whiskers on it, which will shorten the peeling time. Wash yam with water under the faucet and peel it quickly. Peel the peeled yam and put it into water mixed with white vinegar to cut off the contact with air. In this way, the cut yam slices will not turn black.

Reference news: Baidu Encyclopedia-Fried Yam with Lycium barbarum and Auricularia auricula