If mung beans are exposed to the air after being cooked, some active substances in them will be oxidized and the color will change from green to red. Avoid opening the lid when cooking mung bean soup, and it is best to open it when drinking. After being boiled for a short time, mung bean soup becomes greener, with good summer heat relieving effect and poor heat clearing effect. However, when mung beans are cooked for a long time, the soup color is turbid, the effect of cooling off summer heat is poor, and the effect of clearing heat and detoxifying is good. Alkali will turn red. References:

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