What caused this "lunar egg"?

A friend boiled this egg using the Food Lab method, and it came out like this: with a ton of little perfect craters like some kind of cartoon moon. He's never seen anything like this before, and neither have I. He did not make pinholes in it or crack the shell or do anything not described in the cooking method. Also, he's used that way of making boiled eggs before and this hasn't happened.

The method is as follows:

Pour the water into a 3-quart saucepan, cover, and bring to a boil over high heat. Using a large slotted spoon or spider, carefully lower the eggs into the boiling water and cook for 30 seconds. Add the ice cubes and allow the water to return to a boil (be patient, this could take a few minutes) then reduce below a simmer, about 190º. Cook for 11 minutes. Drain the eggs.

What causes a hard-boiled egg to turn out like this?

eggs hard-boiled-eggs

Best Answer

I'm not 100% sure on why this happened, but I know what those "craters" are. They are where there have been bubbles of gas (likely air) definitely under the shell, but possibly under the membrane too. I see things like this on a regular basis in agar plates used for microbiology.

There could be two causes of this that I can think of:

A minor leak in the shell, maybe not visible to the naked eye, but enough that when the eggs were lowered into the boiling water, the gas expanded and bubbled away from the gas entry site. If you look closely and rotate the egg you may be able to see a higher concentration of craters nearest where the entry was. You may have seen a trail of bubbles coming off an egg shell when heated slowly in pre-boiling water - that's the gas escaping from a pin-point hole. If the egg were lowered into boiling water fast enough, with the hole down, the heat would seal the hole by congealing the white and the gas would be forced up and away from the hole into the egg.
The air pocket at the end of the egg ruptured its membrane and small bubbles of gas from that spread around the surface. Same mechanism as above, just different source of gas.

Now I wonder if it can be recreated experimentally? - I bet those things would make a cafe famous if it could be done consistently. A small gauge hypodermic (26+) needle might work.