Why Do My Hard-Boiled Eggs Have Green Yolks?

Tell us if this sounds familiar: you decide to make deviled eggs for a party or potluck, you boil a dozen, peel the shells, slice the eggs open…only to discover that the yolks have turned a sickly shade of green. That color change can diminish the enthusiasm of even the biggest hard-boiled egg enthusiasts. So what causes yolks to go from bright yellow to green? Does the new color have anything to do with how the egg tastes or raise any food safety concerns? Are there ways to avoid the color change entirely? Experts share answers to all of these questions.

Meet the Experts

Bryan Le, Ph.D is a food scientist and author of 150 Food Science Questions Answered

Jennifer Pallian is a registered dietician, food scientist, and founder of Foodess

Lisa Steele is founder of Fresh Eggs Daily and author of the Fresh Eggs Daily Cookbook

Why Yolks Turn Green

The green color happens when the boiling process releases sulphur.

First and foremost, we want to shut down any concerns that green yolks in boiled eggs indicate a problem with the eggs themselves. Our experts assure us that this doesn’t mean that the eggs are past their prime; the shift in hue is just the result of a natural chemical reaction prompted by the boiling process. “The green color that appears on hard-boiled egg yolks is caused by a reaction between iron in the yolk and sulfur in the egg white,” explains Jennifer Pallian, founder of Foodess.

Bryan Le, Ph.D. provides a more detailed breakdown of what’s happening with those yolks: “Egg whites contain a relatively high concentration of cysteine and methionine, two amino acids that contain sulfur. When boiled, these amino acids break down and release hydrogen sulfide and other sulfur-containing gases. The hydrogen sulfide reacts with the iron content of the egg yolk, which precipitates into iron sulfide, a green-colored mineral. Hydrogen sulfide can also react with iron in the cooking water to give this product. This is what gives boiled eggs their greenish color.”

Is It Safe To Eat Green Yolks?

It’s safe to eat green egg yolks, but if you don’t like the way that they look, you can reduce the color change by putting the boiled eggs in cold water.

According to Lisa Steele, chicken keeper and founder of Fresh Eggs Daily, the green yolks are “harmless and perfectly fine to eat.” However, she does acknowledge that they “make for less than perfect deviled eggs!”

Fortunately, there’s an easy workaround that will yield photo-ready hard-boiled eggs. “[The green color] can be avoided by not overcooking the eggs and by cooling them in an ice bath immediately after cooking,” says Pallian. The ice bath’s cold temperature can interrupt the sulfur-producing reaction and halt the color change.

How To Prevent Green Yolks

Softening and filtering the water used to boil the eggs can also help prevent the green yolks.

Chilling the eggs right after boiling can stave off the greening of the yolks, but if you’d like some extra insurance, Le has a few suggestions for the water that you use to boil. “Eggs should be boiled in water that has been filtered and softened to avoid high concentrations of iron in the cooking water. Otherwise, water that has been distilled or gone through reverse osmosis can be used,” he recommends. An even easier preventative measure is “hard-boiling in lower temperature water, to avoid reaching the temperature in which the sulfur-rich amino acids decompose.”

Related: How To Make Perfect Hard Boiled Eggs

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