A floating egg

I just put several eggs in a pot, for hard-boiling. They are all nestled on the bottom of the pot, like good eggs are supposed to . . . except for one, that’s floating. Why would an egg float?

It’s rotten.

Mostly it’s because bacterial activity has caused enough decomposition that the egg has become lighter because of gas losses through the shell. I’d throw it out, eggs are pretty cheap.

Thanks. I already threw it out, just in case.

Makes ya wonder how many eggs you’ve eaten that, had you immersed, would have floated, eh?

No, mostly it’s just because it has a bubble of air in it. It’s normal for perfectly good eggs to float a little. You don’t have to worry about rottenness unless it’s floating high, with (say) a third of the egg above the water line.

So could it be true that, if an egg doesn’t float, it’s necessarily OK to eat?

Ummmmm . . . if an egg loses gas, wouldn’t it tend to sink?

If it’s losing mass and staying the same size, it’s getting less dense, whatever the state of the lost mass. However, you might also consider the source of the gas. The shell isn’t completely impermeable. It generally doesn’t let fluid through, but gas will diffuse through it. During decomposition, some of the fluid contents of the egg are turned into gas, probably under a slight amount of pressure. That escapes, and is also eventually replaced by an air bubble at normal air pressure through diffusion.

By the time I get around to using eggs, they sort of stand on end. I’d think a bit before using one that actually floated.

If you boil them in salt water, the fresh eggs will float, too, BTW.