What you see: A dented, cracked egg; its contents may or may not appear to have spilled out
What it is: The dent suggests that both the shell and the egg's membrane layer broke, making it easier for pathogens to enter.
Eat or toss: This depends on when the crack occurred. If the egg was jostled at home or on your way back from the store, then fully crack it open into a dish, keep it covered in the fridge and use within two days. But if you don't know when the crack occurred, the egg could be contaminated and you should toss.
In this egg, both its hard shell and the protective membrane just beneath appear to have broken, making the egg more vulnerable to invading bacteria. Just how vulnerable?
"For microorganisms, a crack in an eggshell is like the grand canyon,” said Deana R. Jones, a research food technologist at the Egg Safety and Quality Research Unit of the U.S. National Poultry Research Center. And if the membrane is broken as well, she says, “you have basically made this superhighway for anything to get in there. Anything and everything.”
The USDA calls such eggs “leakers” and deems them inedible, said Jones, whose research center is part of the federal agency.
But what exactly is the threat?
Since all eggs have a risk of salmonella bacteria, which is killed instantly at 165 degrees Fahrenheit or after several minutes at 145 degrees, you might think that simply cooking this egg would be enough.
But a hot oven or stovetop can't protect you from the hazards of such an egg, Jones said. While scientists studying eggs know that salmonella is the villain to beat (pun intended) in intact eggs, the field expands considerably when you’re talking about a “leaker” egg. For example, some bacteria generate sickening toxins that aren’t inactivated by heat. Such bacteria might normally be held off by the eggshell and membrane, as well as by chemical and structural defenses in the liquid egg white. But exposure to air from a significant crack will cause the egg white to thin and its defenses to rapidly diffuse. If bacteria can overcome the egg's natural barriers and arrive at the nutrient treasure trove of the yolk, they will start to proliferate like crazy.
“The yolk is where they want to be because that’s like a spa day,” Jones said. “It’s got everything they desire.”
But what if the egg isn't leaking?
If it's just a hairline crack and there's no indication that the membrane has been broken, then you'll want to make sure to cook the egg thoroughly (skip the runny yolk or hollandaise sauce). What Jones calls a "thermal kill," should be sufficient.
However, in the egg pictured above, the dent suggests that the membrane was broken. Even though nothing is leaking at the moment, North Carolina State University poultry specialist Ken Anderson points out some egg white could have leaked and then dried. You have no way of knowing unless you’re positive that the break happened between the store and your home. If you're certain that the crack is fresh, then you can eat the egg, but with a couple precautions. You'll want to thoroughly cook it—either right away or within a couple days (keep it in a covered dish in the meantime).
All bets are off
Food safety experts view the risks from “leaker” eggs as so clearcut that I couldn't find much research on the specific possible outcomes of eating them, aside from the salmonella risk. Of course, such illnesses would likely happen in isolation and would probably escape documentation. Sickened people might not even know what caused their issues. So, when you're staring down a leaker, and don't know how its fractured history, the best answer is "toss."
“There’s too many variables to be able to say ‘I know exactly what happened to this egg and exactly when it started leaking and exactly what it’s been exposed to and exactly how it’s been handled,'" Jones said. "There’s no way to know exactly what the exposure has been….therefore it’s deemed inedible.”
Deana R. Jones. Research Food Technologist. Egg Safety and Quality Research Unit. U.S. National Poultry Research Center. USDA Agricultural Research Service.
Kenneth E. Anderson. Professor, Poultry Extension Specialist. Director, North Carolina Layer Performance and Management Program. Prestage Dept. of Poultry Science. North Carolina State University
Is it Safe to Use Eggs That Have Cracks? Egg Safety Center.
Mechanisms of egg contamination by Salmonella Enteritidis. Inne Gantois, Richard Ducatelle, Frank Pasmans, Freddy Haesebrouck, Richard Gast, Tom J. Humphrey, Filip Van Immerseel, FEMS Microbiology Reviews, Volume 33, Issue 4, July 2009, Pages 718–738.
Death of Staphylococcus aureus in liquid whole egg near pH 8. Ng H, Garibaldi JA. Appl Microbiol. 1975 Jun;29(6):782-6.
Egg white versus Salmonella Enteritidis! A harsh medium meets a resilient pathogen. Baron, F.; Nau F.; Guérin-Dubiard, C.; Bonnassie S.; Gautier, M.; Andrews S.; Jan, S.; Food Microbiology. 2016 Feb.
It's the incredible, inedible egg!