Sour mung bean soup shows that it has gone bad and can't be eaten. Mung bean soup is rich in protein, starch and water. In an environment with suitable temperature, such as high temperature weather, when the mung bean soup is placed at room temperature, microorganisms such as bacteria will multiply for a long time, and protein and carbohydrates in mung beans will decompose to produce some mycotoxins and sour substances, so the deteriorated mung bean soup will have sour taste and odor.

Mung bean is the seed of leguminous plant mung bean, also known as green adzuki bean (named for its blue-green color), wild bean, cultivated bean and so on. It has been cultivated in China for more than 2000 years. Native to India and Myanmar. Now it is widely planted in East Asian countries, but also in Africa, Europe and the United States. China, Myanmar and other countries are the main exporters of mung beans. Seeds and stems are widely eaten. The role of mung bean in clearing heat is in the skin, and the role of detoxification is in the meat. Mung bean soup is a family's regular summer cool drink, suitable for all ages. Traditional mung bean products include mung bean cake, mung bean wine, mung bean cake, mung bean paste, mung bean powder skin and so on.