When an egg is placed in water and floats, it often prompts questions about its age and whether it is still suitable for consumption. Understanding the reasons behind this phenomenon can help in determining the quality of eggs before use.
The Science Behind a Floating Egg
The shell of an egg is porous, allowing for gas exchange. As an egg ages, moisture from its interior slowly evaporates through these pores. This continuous loss of moisture causes the contents inside the egg to slightly decrease in volume.
As moisture exits, air simultaneously enters the egg through the same pores, accumulating in a small pocket known as the air cell. Its size increases proportionally with the egg’s age. A newly laid egg has a very small air cell, often less than 1/8 inch.
The increase in the volume of air, which is less dense than the egg’s liquid contents, reduces the egg’s overall density. A fresh egg is denser than water and will sink to the bottom of a bowl, often lying on its side. An older egg, with its larger air cell, becomes buoyant enough to float, as its density becomes less than that of the water.
Is a Floating Egg Safe to Consume?
A floating egg indicates that it is older, but this does not automatically mean it is spoiled or unsafe to eat. Spoilage in eggs is typically caused by bacterial growth, which produces gases and distinct odors. While a floating egg has a larger air pocket, it may still be perfectly edible if it has been stored properly and shows no other signs of spoilage. The most reliable indicator of an egg gone bad is its smell.
If an egg floats, it should be cracked open into a separate bowl for a visual inspection and a “sniff test.” If the egg emits a strong, foul, or sulfuric odor, it has likely spoiled and should be discarded. The appearance of the white and yolk, such as extreme runniness or discoloration, can also suggest spoilage, but the smell is the most definitive sign.
Beyond the Float Test: Other Freshness Indicators
While the float test offers a quick assessment of an egg’s age, other methods provide a more comprehensive picture of its freshness and edibility. Checking the expiration or “sell-by” date on the carton provides a general guideline, though eggs can often remain good past these dates if refrigerated properly. Another indicator is the egg white’s viscosity. When cracked onto a flat surface, a very fresh egg will have a thick, somewhat opaque white that holds its shape closely around the yolk, while an older egg’s white will be thinner and spread out more.
The position and firmness of the yolk also offer clues. In a fresh egg, the yolk will be round, firm, and centrally located. As an egg ages, the yolk may appear flatter and less firm. Additionally, a gentle shake can reveal freshness; a fresh egg will make little to no sound, whereas an older egg with a larger air cell and thinner white may produce a noticeable sloshing sound.