You can determine the age of an everyday egg without cracking it, thanks to the 'Float Test.' Eggshells are porous, allowing air to pass through. Inside every egg, there is a small air pocket between the shell and the membrane. As an egg ages, moisture evaporates through the pores of the shell and is replaced by air, making the air pocket larger. This increases the egg's buoyancy. A very fresh egg will sink and lay flat on its side at the bottom of a glass of water. A slightly older egg will sink but stand on one end. An egg that floats to the surface is very old and has likely spoiled, as enough air has entered to make it lighter than the water.