The reason this test works has to do with the air pocket inside the egg. As an egg ages, the air pocket grows, causing the egg to become more b buoyant. Think of it like a balloon - when it's inflated, it floats, but when it's deflated, it sinks.
When you put an egg in water, the density of the egg is compared to the density of the water. If the egg is denser than the water, it will sink, but if it's less dense, it will float. It's kind of like when you're on a boat, and you throw a life jacket into the water - it floats because it's less dense than the water.
But what if the egg doesn't sink or float - what if it stands on its end instead? This is actually a sign that the egg is not as fresh as it could be, but still safe to eat. It's like when you're at a restaurant, and you order a medium-rare steak - it's not fully cooked, but it's still edible.
Egg Test in Water How to Tell If Eggs Are Fresh
