Analysis of the reasons why mung bean porridge turns red: 1. The principle of mung bean porridge turning red is very simple. It is the result of oxidative polymerization of phenolic substances dissolved from the skin of mung beans in mung bean soup under the action of oxygen in the air. Therefore, it is easy to change color when cooking mung bean porridge with the lid open, but it is not easy to change color when cooking mung bean porridge in a pressure cooker. 2. Cooking mung bean soup is also related to the water quality. The higher the alkali content of the water, the heavier the red color will be. For example, the water in the north is harder and contains more nitriles, so mung bean soup tends to turn red when cooked. If the local water quality is poor, you don’t need to use tap water. You can also use purified water to cook mung beans or boiled water. Just don’t use raw tap water. 3. If the pot lid is closed, the mung bean soup may turn red if it is simmered for too long. 4. If you use aged mung beans, the mung bean soup will definitely be red. 5. Too much water and too little mung beans can turn red easily. 6. If the container used to cook mung bean soup touches oil, it will easily cause the phenomenon of "red soup". 7. Use an iron pot when cooking mung bean soup. The iron is peroxidized to form trivalent iron, so it appears red.