A translucent star pattern on your egg?
What you see: A translucent spiderweb or shatter pattern on your egg; you may not see an apparent crack. What it is: The shell is slightly cracked, but the membrane around the egg white is still intact. Eat or toss: Eat! But prioritize eating this egg and make sure to cook it thoroughly. It's more vulnerable to pathogens than others in your carton.
Two weeks ago we wrote about how eggs with breaks in both the shell and the inner membrane were too exposed to outside pathogens for safe eating. But with a crack that's only shell-deep, this egg can be salvaged.
In its battle against invading bacteria, the egg has several layers of protection. The first is a clear coating, known as the cuticle, which flakes away over time; and also comes off when eggs are industrially cleaned (a required practice in the United States). Next is the shell. Underneath that are layers of membrane (that skin you often encounter when peeling boiled eggs). Below the membrane layers is the egg white, which comes loaded with chemical defenses and an overall structure hostile to invading microbes.
In the egg pictured here, the shell may appear intact, but the spiderweb shatter pattern means it cracked. This egg might have collided with its carton neighbor during transit, or otherwise been jostled on its journey from farm to you. The egg also could have come from an older or stressed hen, which would be more likely to lay a weaker shelled egg.
The tiny cracks allowed moisture to creep in, which created that gray pattern.
Salvageable, but needs a hard cook
Any pathogens lurking on the shell’s surface now face one less barrier to getting inside the egg. And with more exposure to air, the egg’s internal defenses will weaken faster. Bacteria like salmonella, which causes the food-borne illness most associated with eggs, won't become a big threat overnight, but the longer this egg sits in the carton, the more likely it's hosting a growing party of microbes you’d rather not meet.
It “doesn’t mean you have to be like, ‘I absolutely have to throw this away,’” said Deana R. Jones, a research food technologist for the Egg Safety and Quality Research Unit of the U.S. National Poultry Research Center. But, since the crack could have facilitated a heightened bacterial load in the egg, you’ll want to heat it to 165 degrees Fahrenheit or keep it at at least 145 degrees for several minutes—that's what it takes to kill salmonella bacteria.
If a hairline crack makes you squeamish, throw it away, Jones advised, but baking or a hard scramble where the yolk firms up should be fine. Any preparation with a runny yolk, for example, would be risky, and once the yolk got hot enough to fully mitigate the risk, it the heat would defeat the culinary art of such a dish. Rather than the runny capsule of gold that makes poached and over-easy eggs so delicious, if you reached the temperature guarenteed to kill salmonella, you'd get a harder and drier yolk.
A *riskier* runny yolk Even when you're cooking an egg with a perfect shell, Jones noted that a runny yolk always carries a small risk of salmonella. But given the care the U.S. food system takes to keep the bacteria away from eggs and to maintain a cold chain, and that it would probably take more than a trace of salmonella to sicken a healthy person, the risk is tolerably low for many people.
“Everybody needs to understand that there is a risk-reward association that each person has to make themselves,” she said.
So, eggs with hairline cracks are slightly more vulnerable to pathogens, but, like regular eggs, you can mitigate the risk with thorough cooking. Farmers send such eggs to the “egg products” market where they will be pasteurized to kill pathogens and then directed to large-scale uses like industrial baking, cafeterias or processed foods.
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, Ph.D. Professor, Poultry Extension Specialist. Director, North Carolina Layer Performance and Management Program. Prestage Dept. of Poultry Science. North Carolina State University Cracked Eggs and Your Small Flock of Laying Hens. Commercial Poultry. Manitoba government. Determination of the quality of stripe-marked and cracked eggs during storage Yu Chi Liu, Ter Hsin Chen, Ying Chen Wu, and Fa Jui Tan. Asian-Australas Journal of Animal Sciences. Vol. 30, No. 7:1013-1020 July 2017. Critical points on egg production: causes, importance and incidence of eggshell breakage and defects. Mazzuco, Helenice and Bertechini, Antonio Gilberto. Ciênc. agrotec. [online]. 2014, vol.38, n.1 [cited 2020-04-30], pp.07-14. Maintaining Egg Shell Quality. Dr Lokesh Gupta. The Poultry Site. March 2008. Factors Influencing Shell Quality. Dr. Lokesh Gupta. The Poultry Site. March 2008.
Food Microbiology: An Introduction. Karl R. Matthews, Kalmia E. Kniel, Thomas J. Montville. Fourth Edition. ASM Press. 2017. p. 255 - 257.
To prepare this series of egg posts I wanted to ask the scientists all my questions at once. But instead I scheduled a series of interviews, so as not to put all my eggs in one asked-it.