How Can You Tell a Boiled Egg Has Gone Bad?

The clearest sign that a hard-boiled egg has spoiled is a sharp, sulfur-like odor after it is peeled; this smell is much stronger than the faint odor of a raw egg and is the most reliable sign of spoilage.

What visual changes should you look for?
The white of a peeled hard-boiled egg normally looks glossy and smooth. If gray-green spots, a slimy surface, or small colored spots appear, the egg is no longer safe. A thin greenish-gray ring around the yolk is not spoilage; it is a harmless sulfur-iron reaction caused by boiling the egg for too long. It is harder to tell whether an egg has spoiled while its shell is still on, so if you plan to store hard-boiled eggs for a long time, leaving the shells on offers more protection and makes signs of spoilage easier to notice, since a cracked shell or a bad smell can also be detected from the outside.

How long should they be stored?
Peeled hard-boiled eggs generally keep for 5–7 days in a covered container in the refrigerator; unpeeled eggs can be stored a little longer. A hard-boiled egg left at room temperature for more than 2 hours should be discarded for safety, even if its appearance has not changed. Storing hard-boiled eggs in a container of water is a common mistake; this method spoils them quickly because a moist environment speeds bacterial growth. The right method is to pat peeled eggs dry with a paper towel and store them in a covered container in the refrigerator. Texture is another clue: the white of a freshly boiled egg is slightly springy and cuts cleanly, while the texture of a spoiled egg softens and falls apart; its yolk turns gooey and foul-smelling rather than simply runny.

How do transport and different levels of doneness change things?
It is important to transport hard-boiled eggs without breaking the cold chain, such as in a picnic or work lunch bag. An egg left at room temperature for more than 2 hours in a bag without an ice pack should not be eaten, even if it is brought back home. When eggs are cut up and added to a salad, the other ingredients, such as mayonnaise or yogurt dressing, also affect how quickly it spoils, so egg salads should be eaten promptly. The yolk of a soft-boiled egg remains runny, so it has a slightly higher risk of spoilage than a hard-boiled egg; soft-boiled eggs should be eaten immediately after cooking and are not suitable for long-term storage.

Freshness is especially important in meals prepared for someone with an egg allergy or a sensitive stomach or digestive system. Do not taste one egg with a questionable smell to test it; discard it immediately. If a large batch of boiled eggs—for example, one dozen—is all peeled at once and placed in the same container, the odor from one that starts to spoil early can spread to the others. Instead of storing a large quantity of hard-boiled eggs in one container for a long time, divide them into small groups based on how quickly they will be eaten; this helps protect the eggs that remain fresh and makes it easier to spot a spoiled one early. On eggs dyed for a holiday or decoration, the dye on the shell may partly mask an odor. Even if these eggs are displayed as decorations, they should not be left out of refrigeration for long; if they will be eaten, put them back in the refrigerator after dyeing.