1, in the simmering green bean soup should be covered with a lid, minimize the contact area of green beans and oxygen, to avoid oxidation, so that it will not polymerize into a darker color.
2, with pure water simmering, not easy to discoloration, the color will be more green, because tap water contains more other substances, and green beans together with the cooking is very easy to react, produce other dark-colored substances.
3, the study found that the acidity and alkalinity can also greatly affect the soup discoloration effect, alkaline water is more likely to make the green bean soup discoloration, so when cooking can be added to the water half a spoonful of white vinegar, or squeeze a few drops of lemon juice, weakening the alkaline of the water, you can prevent discoloration.
Additionally to remove the skin of the green beans, you need to soak the green beans for a few hours, and then rub them with your hands, the force should not be too large, and keep rubbing until the skin of the green beans floats out of the water.