Many people have wondered why some eggs sink in water while others float. This simple observation offers insight into an egg’s physical properties. It reveals the subtle changes that occur within an egg over time. This common kitchen experiment provides a practical way to understand an egg’s internal state.
The Science of Egg Buoyancy
A fresh egg typically sinks and lies flat on its side when placed in a glass of water. This occurs because a fresh egg is denser than the water surrounding it. The interior of a newly laid egg is almost entirely filled with its contents, containing very little air, which contributes to its higher density compared to water.
Eggshells are porous, with microscopic pores that facilitate the exchange of gases and moisture with the surrounding environment. Over time, as an egg ages, moisture from its interior evaporates through these pores. Air from the outside permeates inward to replace the lost moisture.
This continuous exchange leads to the gradual enlargement of the air cell, a small pocket of air usually found at the large end of the egg. As the air cell expands, the volume of air inside the egg increases, which decreases the egg’s density. When the egg’s density becomes less than that of the water, it begins to rise and float.
What Egg Buoyancy Reveals About Freshness
The behavior of an egg in water indicates its age. A very fresh egg, with a minimal air cell, sinks completely to the bottom and lies flat on its side. This horizontal position signifies minimal air absorption and peak freshness.
As an egg ages, moisture loss and air absorption cause the air cell to expand. This increased buoyancy leads the egg to stand upright on its wider end at the bottom of the container. An egg in this position is suitable for use but is no longer newly laid.
An egg that floats just above the bottom of the container has an even larger air cell, indicating further aging. If an egg floats entirely on the surface of the water, it indicates considerable age. Its air cell has expanded significantly due to prolonged moisture loss and air intake.
Are Floating Eggs Safe to Eat?
A floating egg indicates age, but it does not automatically mean the egg is spoiled. The float test gauges an egg’s freshness based on its air cell size, not the presence of harmful bacteria. Spoilage is caused by bacterial growth, which is distinct from air cell expansion.
To determine if a floating egg is edible, the “sniff test” is the most reliable method. Once cracked, a spoiled egg will emit a distinct, unpleasant sulfurous odor. A fresh egg has little to no smell.
Beyond odor, visually inspect the egg’s appearance after cracking it into a bowl. Look for unusual discoloration, such as green or pink hues, or a watery white. If the egg passes both the sniff and visual tests, it is generally safe to use, often preferred for baking or hard-boiling due to its altered texture.