1, in the cooking of mung bean soup will change color, first of all, because the mung bean contains polyphenols, this material and oxygen after full contact with the oxidation reaction will become red or brown, and the longer the color will be deeper, and may be because of the water is relatively hard, the water is relatively hard, then, is rich in metal ions, this material is also polyphenols will react to the substance, resulting in the color of red. This substance will also react with polyphenols, causing the color of green bean soup to become red.

2, in addition to this there is a reason, is that a lot of people use iron pots and spoons to cook green bean soup, and iron pots and spoons also contain metal ions, so the chemical reaction with the green beans will become red, so in the reading of these are to pay attention to.