Why do your boiled potatoes turn gray?

The gray discoloration of boiled potatoes is caused by a chemical reaction between the iron in the water and the polyphenols in the potatoes. Polyphenols are compounds found in plants that are responsible for their color and flavor. When polyphenols come into contact with iron, they oxidize and turn brown. This reaction is accelerated by heat and light, which is why boiled potatoes are more likely to turn gray than potatoes that are cooked in other ways. To prevent potatoes from turning gray, you can cook them in salted water or add a small amount of vinegar to the water. Salting the water will help to reduce the amount of iron that is available to react with the polyphenols, while vinegar will help to slow down the oxidation process.