What you see: You just tried to crack a raw egg and somehow didn’t break all the way through. There’s a rough, translucent layer just below the shell.
What it is: The egg’s membrane.
Eat or toss: Eat! This egg is perfectly fine.
An intact membrane on a cracked, raw egg
Crack open an egg during normal circumstances and the shell and the membrane layer underneath bust open all at once.
But not this time!
Whether it was a weak cracking force or an extra robust membrane, or something else, this egg’s shell cracked, but the membrane hung on tight. So, some shell flaked off and we get a sneak peak at the network of protein fibers that makes up the egg’s membrane layers.
Clear, leathery layer under eggshell contains keratin
That protein network includes keratin, which is also found in human hair, as well as horns, hooves and claws. The protein fibers line up a bit like fiberglass, egg researcher Deana R. Jones told me, making for a strong protective pouch that blocks potential invaders.
Eggs actually have two membrane layers, one that sticks to the shell, and another that sticks to the egg white. In the egg pictured above at least the inner membrane, and possibly both, remained intact.
“There’s nothing wrong with this. It may just seem a little bizarre,” said Jones, a research food technologist at the U.S. Department of Agriculture’s National Poultry Research Center.
Hard to say why the egg’s membrane didn’t break
From the image, she said it was difficult to pinpoint exactly why this membrane held on so tightly, or why the shell so easily flaked off. One possibility is that the egg was laid by an older hen. As chickens age, they produce eggs with thinner shells.
Or, maybe this is just the style of egg that this particular hen tends to lay.
“Each hen uniquely makes her own eggs,” Jones said.
- Deana R. Jones. Research Food Technologist. Egg Safety and Quality Research Unit. U.S. National Poultry Research Center. USDA Agricultural Research Service.
- Anatomy of an Egg. Accidental Scientist. The Science of Cooking. Exploratorium.
- Keratin. Britannica.
- The Different Parts of An Egg. Sauder’s Eggs.
There’s nothing insane in this membrane