2. The red rust spot on kidney bean is called bean anthracnose, which produces spindle-shaped or oblong spots on the stem of kidney bean, which are purplish red at first and sunken, and when it is serious, it harms the pod and forms reddish-brown spots, which is a fungal disease. Therefore, kidney beans are rusted and can't be eaten, which will cause gastrointestinal discomfort.

3. Rusting of kidney beans often eaten in daily life is generally caused by long storage time or inaccurate storage location. Kidney beans are often stored in some dark and humid places and are prone to rust, so it is best to store them in a dry place or eat them on the same day, so don't store them for too long and cause deterioration.