Whether an egg sinks or floats in water depends on the individual egg. When placed in a bowl of water, some eggs will immediately sink to the bottom, while others will gently float on the surface. This observation provides clues about an egg’s age. The varying behavior of eggs in water stems from subtle changes occurring within them over time.
The Science Behind Egg Sinking or Floating
An egg’s ability to sink or float is governed by its density relative to water. Density is a measure of mass per unit volume. A fresh egg typically has a density greater than that of water, causing it to sink. Eggshells are porous, containing thousands of microscopic pores. These tiny openings allow for the exchange of gases and moisture between the egg’s interior and the surrounding environment.
As an egg ages, water inside its shell evaporates through these pores, and air enters. This process leads to the gradual enlargement of the egg’s internal air cell, usually at the wider end of the egg. The increasing volume of air, which is less dense than the egg’s liquid contents, reduces the egg’s overall density. When enough water has evaporated and the air cell has expanded, the egg’s density can become less than that of the water, causing it to float.
What Your Egg’s Behavior Tells You
The egg float test provides a practical way to gauge an egg’s age. If an egg sinks to the bottom and lies flat on its side, it indicates a fresh egg with a small air cell. An egg that sinks but stands upright on its narrower end suggests it is a few weeks old; its air cell has grown, but it is still suitable for consumption.
When an egg floats to the surface, it signifies an older egg with a larger air cell. While a floating egg is indeed older, it is important to understand that it is not necessarily spoiled. An older egg with an enlarged air cell may still be safe to use. However, if a floating egg also emits an unpleasant odor when cracked, or if its contents appear discolored, it has likely spoiled due to bacterial growth and should be discarded. The float test primarily indicates age, while a “sniff test” after cracking the egg is the most reliable way to confirm spoilage.