1. Generally speaking, mung bean soup will change color when you are young. The freshly cooked mung bean soup is often thick and green. After a while, you will find that the mung bean soup in the pot is already light red. The reason is nothing more than that the polyphenols in mung bean skin act in the air, leading to discoloration.

2. Many families are used to boiling mung bean soup with pure water, and the boiled mung bean soup often does not change color for a long time. Mung bean soup boiled with tap water often swims to the bottom of red soup almost every minute after it is cooked. Scientific research shows that the different PH value of tap water will also lead to the length of discoloration time. If the tap water is acidic, the color of the boiled mung bean soup changes little. If tap water is alkaline, it tends to turn red when exposed to air.

3. When cooking mung bean soup, iron can easily catalyze the oxidation of various vitamins and other substances, such as the oxidation of polyphenols in mung bean skin. Therefore, it is best not to cook mung bean soup in an iron pan, otherwise it will produce thick red mung bean soup.