Why some hard-boiled egg yolks have a gray ring around them

Hard-boiled eggs might be one of the most versatile ingredients in the kitchen. On their own, hard-boiled eggs make a tasty and high-protein snack or meal, and they can provide a substantial foundation for classic recipes like deviled eggs and egg salad.

Making the perfect hard-boiled egg can be a tough shell to crack, though. It’s tricky to determine how long the eggs should remain in the boiling water, and then it can seem impossible to get the stubborn eggshells to peel off cleanly (check out our tips on making quick work of those eggshells).

But even if you’ve taken all the proper steps, you still might notice something unusual when cutting open that hard-boiled egg: There’s a colored ring around the bright yellow yolk. It may look gray or even green, but there’s no mistaking the halo effect around the center of your tasty snack.

Does this discolored ring around the yolk mean your eggs are spoiled? Did you over-boil them? Are these oddly hued eggs safe to eat? We’ve done a little research in our scramble to find the answers to these questions.

An Egg’s Gray Ring Is All About Chemistry

The acts of cooking and baking are actually sciences. Anytime you take an ingredient and mix it with something else or alter its temperature, the original ingredient’s physical or chemical properties can change. Even something as simple as a hard-boiled egg is a complicated experiment happening inside a thin shell.

According to Science Focus, the reason hard-boiled eggs can form those gray or green rings has to do with the eggs’ chemical composition. A raw egg is made up of 92% water, plus some proteins that are all held together (and separate from the yolk) by chemical links made of sulphur.

When heat is applied to the egg as it boils, the sulphur links break down and can start to change into hydrogen sulphide, which then reacts with the iron in the egg yolk to produce iron sulphide.

That iron sulphide is what creates the odd color around the yolk. So, if you see these little rings in your hard-boiled eggs, it simply means the eggs may be slightly overcooked.

It is possible to avoid those unsightly rings by following some egg-boiling best practices, such as using a timer and placing your eggs in an ice bath right after boiling them.

Are Hard-boiled Eggs With Gray Rings Safe To Eat?

Those funky, discolored rings in your hard-boiled eggs may make you wonder if they are harmful to eat. Fortunately, the United States Department of Agriculture (USDA) website clearly states the green or gray color in the eggs is “safe to consume.”

So, if you happen to see a little ring around your egg, don’t worry! You can eat it without fear and try to get that perfectly prepared egg next time.