Because natural pigments are unstable, afraid of light, heat and oxygen, long-term cooking and overheating will destroy chlorophyll in food, thus changing the color of food.

1) Mung bean soup is often boiled into dark red, such as washing mung beans with cold water, putting them in a container, and then putting them in hot water; If you need to add water during cooking, you still need to heat the water, so that the boiled soup is green.

2) If the peas are boiled when cooking, they will turn red after a while. This kind of mung bean soup can relieve summer heat and quench thirst, and peas can still be eaten.

If the beans are not boiled in water and baked in fire, the natural soup color is yellow-green. This mung bean soup can clear away heat and detoxify, but beans can't be eaten.

3) If edible alkali is added, it will reflect, and generally it will appear red. The purpose of alkali release is to make beans rot easily, but it will lose the nutrition of beans; In addition, if the pot itself has a small amount of alkali, it will also have this kind of reflection (the alkali in the pot is usually tap water)