The household question of whether a floating egg is still safe to eat is a common query regarding food storage. The simple answer is that an egg that floats in water is significantly older than one that sinks, as the test is fundamentally a measure of an egg’s age, not its spoilage. While an older egg carries a higher probability of deterioration, its buoyancy alone does not confirm that it is spoiled. The float test provides a quick, non-destructive way to estimate the freshness of an egg whose date may be unknown.
Performing the Float Test and Interpreting Results
To perform this test, fill a bowl or glass with enough cold water to fully submerge the egg you wish to check. Carefully lower the egg into the water and observe its reaction.
A very fresh egg will immediately sink to the bottom and lie completely flat on its side. This position indicates that the egg’s internal contents are dense and that its internal air cell is still very small.
If the egg sinks but stands upright on its pointed end, it suggests the egg is approximately one to three weeks old. While not as fresh, an egg in this position is safe to consume and is well-suited for hard-boiling, as the slightly larger air pocket makes it easier to peel.
An egg that floats completely to the surface of the water is considered very old and should be discarded. This complete buoyancy signals that the internal air cell has grown considerably, changing the egg’s density enough to overcome the density of the water.
Why Eggs Float as They Age
The ability of an egg to float is related to a gradual process of moisture loss and air gain through the shell. The eggshell is highly porous, featuring thousands of tiny pores that allow for gas exchange.
Over time, water vapor and carbon dioxide from the egg’s interior escape through these pores. As moisture leaves the shell, outside air is drawn in to replace the lost volume.
This air collects in a space between the inner and outer shell membranes, known as the air cell. The continuous exchange of moisture for air causes this air cell to progressively increase in size.
Because air is less dense than the egg’s liquid contents, the growing air cell lowers the egg’s overall density. Once the egg becomes less dense than the water, buoyancy causes the egg to float.
Alternative Methods for Checking Freshness
While the float test measures age, other sensory methods are more specific for determining if an egg has spoiled. The sniff test is the most definitive indicator of safety, as a spoiled egg will produce an unmistakable, strong sulfurous odor.
When cracking an egg, the appearance of the yolk and albumen, or egg white, provides clues about its condition. A fresh egg will have a firm, high-standing yolk and a thick, slightly cloudy egg white that does not spread much.
Conversely, an older egg that is still safe to eat will have a flatter yolk and a thin, watery egg white that spreads out across the plate.
Another check is the shake test, where a fresh egg will be silent when gently shaken. An older egg may produce a slight sloshing sound due to the thinning of the liquid contents.