Step-by-step instructions for the bathing water test: To perform the bathing water test, fill a bowl with enough water to completely submerge an egg. Carefully place the egg in the water and observe its behavior. If the egg sinks to the bottom and lies flat on its side, it is very fresh. If it stands upright on the bottom, it is still safe to eat but should be used quickly. If the egg floats to the surface, it is no longer fresh and should be discarded.
Why the bathing water test works: The bathing water test works because of the air cell inside the egg. As an egg ages, moisture and carbon dioxide escape through the porous shell, and air enters to replace them, enlarging the air cell. This makes the egg less dense and provides more buoyancy. A fresh egg has a small air cell and sinks, while an older egg floats with a larger air cell.
