When cooking mung bean soup, the polyphenols in mung beans will dissolve and oxidize, and the color of the soup will change from green to red. This oxidation is not only related to oxygen, but also to water quality. Associate Professor Fan Zhihong, Department of Food Nutrition and Food Safety, China Agricultural University, has done experiments, and boiled mung bean soup with tap water, mineral water, purified water and deionized water respectively. The results showed that the mung bean soup boiled with deionized water was the greenest and remained unchanged for a long time. Mung bean soup cooked with tap water soon turned red. In addition, if you cook mung bean soup with tap water, its pH will also affect the color of the soup. The mung bean soup cooked with acidic tap water will change color slightly, and the alkaline one will change color quickly.

In a word, the reason why mung bean soup is cooked red is related to the concentration of metal ions in water and its pH value, and to the oxygen in the air.

How to cook green mung bean soup?

According to the above, if you want to cook green mung bean soup, you must find ways to choose water, utensils and cooking methods. First of all, in terms of water selection, it is best to use pure water. It is best to install a tap water purifier at home. If not, many communities now have drinking stations that can also provide pure water. If the above two conditions are not met, green mung bean soup can also be cooked with tap water, just add a little white vinegar or lemon juice to the water. Secondly, cover the pot cover to reduce the contact area between the soup and oxygen; Finally, in order to reduce the interaction with metal ions, it is best to cook mung bean soup with stainless steel pot or casserole.

Cooking method of mung bean soup

The heat-clearing and summer-relieving ingredients in mung beans exist in the bean skin, so don't remove the mung bean skin when cooking mung beans. When cooking, first boil the water, and then add the mung beans. When boiling again, turn to low heat and cook for 8~ 10 minutes. At this time, the soup is bright green and has the effect of clearing away heat and relieving summer heat. You can filter out the soup and continue to cook the remaining mung beans until they bloom. You can also add rice and millet to cook mung bean porridge.