Because the temperature is too high. At room temperature, the bean sprouts should be watered with warm water of 20-23 degrees for 4-5 hours, and the water should be replenished to keep warm, otherwise the bean sprouts will turn yellow. Fresh mung bean sprouts should not be stored for too long, just put them in the refrigerator 1-2 days. Bean sprouts can make many delicious foods, such as sweet and sour bean sprouts, hot and sour bean sprouts, shredded bean sprouts, fried bean sprouts and so on.