If you've ever found a green ring around the yolk of a hard-boiled egg, you may have wondered if it's safe to eat. While the discoloration is usually harmless, it can sometimes be indicative of a bacterial reaction. To avoid serving unsafe eggs at your next buffet, there are a few things you can do to keep them from turning green.
The first step is to use fresh eggs that have been refrigerated. If possible, purchase them from a local farm or farmer's market where they were likely laid within the past week. Older eggs are more likely to develop bacteria that can cause the greening reaction.
When boiling the eggs, be sure to use enough water to cover them by an inch or two. Add a tablespoon of vinegar or lemon juice to the water before adding the eggs. This will help to prevent them from cracking and also keep any bacteria that might be on their shells from contaminating the inside of the egg.
Once they're cooked, immediately transfer the eggs to an ice bath for about 15 minutes. This will stop the cooking process and help keep them fresh longer. If you're not planning on using them right away, store them in the fridge in a covered container filled with cold water (change it out every day or so).