Mung bean soup is a very common summer drink. Drinking mung bean soup in summer has the effect of clearing away heat, relieving summer heat and reducing inflammation. But some people boil mung bean soup in red. What's the matter? What's the cause of the redness of mung bean soup? Let's get to know.
Why is mung bean soup red?
Red after contact with air
Contact with the air, when cooking mung bean soup, uncoil the pot and cook it, and stir it from time to time. At this time, the main reason for the red color of mung bean soup is that the polyphenols dissolved from the surface of mung bean are oxidized and polymerized under the action of oxygen in the air, thus forming the red color. Therefore, it is better to boil the mung bean soup in one pot to the end to avoid contact with the air.
Turn red after cooking in an iron pot
The flavonoids in mung bean skin may form a complex with darker color after interaction with metal ions, which may change the color of mung bean soup. Although this reaction has no toxic substances, it may interfere with the antioxidant effect of mung bean and the absorption of metal ions. Therefore, when cooking mung bean soup, the iron pot is the most inappropriate, and the casserole is the most ideal.
Discoloration with honey
When the mung bean soup is boiled with honey, the minerals in the honey will form a complex with the polyphenols in the mung bean, the color is mostly soy, black, brown, dark green, etc., which makes the color of the mung bean soup dark and dark. It is suggested that the mung bean soup should not be boiled with honey, and a little bit can be added when eating.
Discoloration after boiling in alkaline water
It is found that the acidity and alkalinity of water can affect the color of mung bean soup. The discoloration of acidic tap water is small, and the discoloration of slightly alkaline tap water is very rapid. The tap water in the north is mostly alkaline water, so the color change of mung bean soup is very fast, and obvious color change can be seen within two minutes. It is recommended to boil it with pure tap water.
How does mung bean soup not change color?
Boil with pure water
So, will the green bean soup turn red? In fact, it's not. Our experiments show that mung bean soup can be kept unchanged for a long time, and the secret of the problem is that the water used to cook beans is different.
Using tap water, mineral water, purified water and deionized water respectively to cook mung bean soup, the result is that the color of deionized water is the greenest, and it will not change for a long time. The color of mung bean soup boiled in tap water changes the fastest. It becomes dark almost every minute after contact with the air, and soon turns red. Obviously, it is caused by different water quality.
We adjusted the tap water to different pH value to cook mung bean soup, and found that the pH value can greatly affect the discoloration effect of the soup. The discoloration of acidic tap water is very small, while that of slightly alkaline tap water is very fast. Most of the tap water in the north is alkaline water, so the color change of mung bean soup is very fast, and you can see the obvious color change within two minutes. However, for deionized water, no matter what pH, the color change is very small.
In this way, we can get a simple way to cook mung bean soup without discoloration - directly with pure water, there is no problem.
Add some vinegar when cooking
If there is no pure water at home, it is not impossible to keep green when cooking mung bean soup with tap water. Just add half spoon of vinegar or squeeze half spoon of lemon juice into the soup to keep the green color in the air for a long time.
The key is not to add too much, let alone make the water sour, just adjust to pH 6.
When cooking, it's better to mix the water first, and then cook the green bean clear soup. It's not easy to change color. Even if stored for half an hour, it can still keep a nice green color.
Cover the pot, cook and drink
When cooking mung bean soup, you should also cover the pot cover to minimize the contact area with oxygen and reduce oxidation. Moreover, the heating time of boiling with boiling water is shorter than that of boiling with cold water, and the oxidation is slightly less; the contact oxygen of boiling with pressure cooker is less, which is conducive to the maintenance of soup color. However, as long as the soup scoops out, they will soon change color.
At the same time, cooking time should also be noted. When cooking mung bean soup, it is difficult to keep its yellow and green color because of the long cooking time and full contact with oxygen. It is advisable to take out the soup boiled within 10 minutes and drink it as soon as possible, because the color of the bean soup is green at this time, and the dissolved substances are mainly the active ingredients in the bean skin, and the oxidation degree is the lowest, and the heat clearing ability is the strongest.
After taking out the soup, don't throw away the rest of the mung bean, you can add boiling water to continue cooking, and cook into mung bean paste, or add rice to cook into mung bean porridge.