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College of Food, Agricultural, and Environmental Sciences


Chow Line: Play it safe with hard-cooked eggs (for 4/8/07)

March 30, 2007

How long can you keep hard-boiled eggs?

You can generally count on hard-boiled eggs to last a week in the refrigerator. Even with its natural (but easily cracked) calcium-carbonate container, a hard-cooked egg is a perishable food, so it shouldn't be kept at room temperature for more than two hours.

Interestingly, hard-boiled eggs don't keep nearly as long as raw eggs, which can last three to five weeks in the refrigerator. There's a good reason for that. When a hen lays an egg, it puts a naturally protective coating on the outside of the shell. The bad news is, during the washing and sanitizing process before packaging, eggs lose that coating. But the good news is, processors replace it with a tasteless, natural mineral oil coating. But there's another piece of bad news: That coating is removed when you hard-boil the egg. So, even if the egg's shell remains uncracked, it still is slightly porous and, without the coating, is more exposed to the elements.

You'll know a spoiled egg when you crack open the shell. Whether raw or cooked, a spoiled egg will have an unpleasant odor. No question about it: throw it out.

On the other hand, don't worry if you see a green ring around the yolk. According to the U.S. Department of Agriculture's Food Safety and Inspection Service, that usually means the egg was overcooked and allowed sulfur and iron compounds in the egg to react on the yolk's surface. Sometimes the green color is traced to a high level of iron in the water used to boil the eggs. If you've ever truly seen "green eggs and ham," it likely means that the scrambled eggs were cooked at too high of a temperature or held on a steam table too long -- they can also develop a greenish cast. Again, don't worry: Though unappetizing, eggs with a green color are safe.

Fresher hard-cooked eggs may be harder to peel. According to the Egg Safety Center, an organization supported by the egg industry, fresh eggs have a smaller air cell, which is located at the large end of the shell between the shell membranes. The older the egg, the bigger the air cell, and the easier the egg is to peel.

To find out how old your eggs are, take a look at your egg carton. Each carton with the USDA grade mark carries a "Julian date," usually on the short end of the carton, indicating the day the carton was packed. The Julian date is a three-digit code representing the day of the year, with 001 meaning Jan. 1 and 365 meaning Dec. 31. The larger the number, the later in the year the egg was packed.

For more information on egg safety, see the USDA fact sheet, "Focus on Shell Eggs," at, or the Egg Safety Center's Web site at


Chow Line is a service of Ohio State University Extension and the Ohio Agricultural Research and Development Center. Send questions to Chow Line, c/o Martha Filipic, 2021 Coffey Road, Columbus, OH, 43210-1044, or

Editor: This column was reviewed by Lydia Medeiros, registered dietitian, food safety specialist for Ohio State University Extension, and associate professor in the Department of Human Nutrition, College of Education and Human Ecology.

To receive a PDF file of Chow Line via e-mail, contact Martha Filipic at

Martha Filipic
Lydia Medeiros