What is the source of Dr. Seuss' Green Eggs and Ham? (Why do hard boiled eggs sometimes have green coated or tinged egg yolks?)
The green color is likely due to iron sulfide. The egg itself is the source of the sulfur and the iron may come from the egg OR from iron rich water in which the egg is boiled. I understand longer cooking tends to underscore the green coating of the iron sulfide; less cooking time makes "cleaner" looking boiled eggs.
You know, I've read that story about Green Eggs and Ham to my son for years (he liked all of those Dr Seuss stories) and didn't get the connection between green eggs and iron sulfide until your post (some 45 years after I quit reading to my son). I just thought the title was one of those "Give it a title that will make people by the book."
The source of inspiration for Dr. Seuss' "Green Eggs and Ham" might not relate directly to the phenomenon of green coated or tinged egg yolks in hard-boiled eggs. However, I can explain the reasons behind the green discoloration in hard-boiled eggs.
The green coating or tinge that can sometimes appear on hard-boiled egg yolks is caused by a chemical reaction between the iron in the egg yolks and sulfur in the egg whites. This reaction occurs when eggs are cooked for an extended period at high temperatures or are stored for too long.
Here's how to avoid green yolks in hard-boiled eggs:
1. Proper cooking time: Overcooking eggs can lead to the formation of green discoloration. To avoid this, cook your eggs for the appropriate time. For large eggs, bring water to a boil, then reduce heat and let them simmer for about 9-12 minutes.
2. Cooling and peeling: Once the eggs are cooked, plunge them into cold water or an ice bath immediately to stop the cooking process. This helps minimize the likelihood of green coloring. Additionally, peel your eggs soon after cooling to prevent them from absorbing sulfur from the air.
3. Storage: If you plan to store hard-boiled eggs, keep them in a covered container in the refrigerator. Avoid leaving them at room temperature for too long as this can contribute to the green discoloration.
By following these precautions, you can enjoy hard-boiled eggs without worrying about green yolks.