Potatoes that turn black after they are boiled do so for a number of reasons, such as undergoing a reaction with the cookware being used, having bruises due to being dropped and being stored in cold conditions. To keep potatoes from turning black, they should not be stored in temperatures under 40 degrees Fahrenheit.
Cookware that contains aluminum or iron can react with the potatoes to change their color. Stainless steel cookware helps prevent this problem.
Cooked potatoes may be soaked in a small amount of lemon juice and covered in a pan to prevent post-cooking reactions that cause discoloration.
Black potatoes are safe for consumption and contain the same amount of nutrients as potatoes that are a normal color.