Discovering a raw egg floating in a glass of water can be a surprising moment, often prompting a question about its edibility. This simple observation, commonly known as the “float test,” is a practical way to assess an egg’s freshness. The phenomenon of an egg floating or sinking is directly related to its internal changes over time.
Understanding Egg Buoyancy
The ability of an egg to float or sink in water is governed by its density relative to the water it displaces. A fresh egg typically sinks and lies flat at the bottom of a container because its contents are dense and contain very little air. Eggshells are porous, allowing for the exchange of gases and moisture with the environment.
As an egg ages, two changes occur that affect its density. First, moisture evaporates from the egg’s interior through its shell pores. Second, air penetrates the shell, accumulating in a pocket at the larger end, known as the air cell. This air cell forms as the egg cools and expands over time. The increasing volume of air, less dense than the egg’s liquid contents, causes the egg’s overall density to decrease, making it more buoyant.
What a Floating Egg Reveals
A floating egg indicates that its internal air cell has expanded due to aging. This means the egg is older, but it does not automatically signify that the egg is spoiled or unsafe to eat. A fresh egg will sink flat, while an egg that is a bit older but still good might sink but stand upright.
The more an egg floats, the larger its air cell, and thus, the older the egg is. While an older egg may not be ideal for dishes requiring a firm yolk or thick white, such as poaching, it is suitable for baking or hard-boiling. The distinction between an old egg and a spoiled egg lies in other indicators, not solely its buoyancy.
Simple Ways to Check Egg Freshness
While the float test provides a quick indication of an egg’s age, combining it with other sensory checks offers a more comprehensive assessment of freshness and safety. The sniff test is reliable; a spoiled egg emits a distinct, unpleasant sulfurous odor, often noticeable before cracking the shell. If no smell is detected with the shell intact, crack the egg into a separate bowl for a clearer sniff test and visual inspection.
Observing the yolk and white after cracking can also reveal freshness. A fresh egg will have a firm, rounded yolk that stands up well, and a thick, somewhat opaque egg white that clusters around the yolk. As an egg ages, the yolk tends to flatten, and the white becomes thinner and more watery, spreading out more easily. Additionally, gently shaking an egg can offer a clue; a fresh egg will not make any sound, whereas an older egg with a watery yolk might produce a sloshing noise.