If you’ve ever boiled eggs and noticed a green or grayish ring around the yolk, there’s usually no reason to panic. The discoloration does not necessarily mean the egg is spoiled. In most cases, it happens because the egg has been cooked too long or at too high a temperature.

The green ring is caused by a natural chemical reaction between sulfur in the egg white and iron in the yolk. When the egg is exposed to prolonged heat, these elements react where the white and yolk meet, creating iron sulfide. This produces the familiar greenish or grayish color around the yolk.

Although the ring may not look appealing, eggs with this discoloration are generally safe to eat if they have been stored and handled properly. The change mainly affects appearance and can sometimes make the yolk slightly firmer or drier. However, an unusual smell or other signs of spoilage are reasons to avoid eating the egg. As the original article explains, “The color change mainly affects the appearance and may slightly alter the texture of the yolk.”

The easiest way to prevent the green ring is to avoid overcooking your eggs. Cooking them for about 9–12 minutes, depending on how well done you want them, can help keep the yolk bright yellow. Moderate heat is also preferable to very high temperatures.

Quick cooling can make an important difference too. Once the eggs are finished cooking, place them immediately in cold or ice water. This stops the cooking process and reduces the chance of continued heat causing discoloration. In short, “a green or gray ring around an egg yolk is usually a sign of overcooking rather than spoilage.” With the right cooking time, moderate heat, and rapid cooling, you can enjoy boiled eggs with a smoother texture and brighter yolks.