A fresh egg sinks to the bottom of a bowl of water and lies flat on its side. An older egg may stand upright or float. Floating is not a sign of a good egg — it is a sign that the egg has lost water and its internal air pocket has grown larger over time.
That single fact answers most of the confusion around the float test. The float test is a rough freshness gauge, not a safety test. An egg can float and still be safe to eat, and an egg that sinks can still be contaminated with bacteria. Understanding why the egg floats — and what floating actually tells you — matters more than the result itself.
Why Does a Fresh Egg Sink in Water?
An eggshell is not solid. It is porous, and it contains thousands of tiny pores that let gases and moisture pass through.
When an egg is first laid, the space between the shell membranes at the wide end is very small. As the egg ages, moisture evaporates through the shell and carbon dioxide escapes. The inner membrane pulls away from the shell, and the air cell at the wide end grows larger.
A larger air cell means more buoyancy. A fresh egg has a small air cell, so it is denser than water and sinks. An older egg has a bigger air cell, so it floats higher. This is basic physics, and it is well established in poultry science and food safety references.
Temperature and humidity during storage affect how fast the air cell grows. An egg kept cool and humid loses water more slowly than one stored warm and dry. This is one reason refrigeration extends freshness.
Do Good Eggs Float Or Sink? What the Float Test Actually Tells You
A good, fresh egg sinks and lies flat on its side at the bottom of the bowl. That is the result you want.
Here is how the results usually break down:
- Sinks and lies flat: The egg is fresh or fairly fresh.
- Sinks but stands upright on one end: The egg is older but likely still fine to eat if it smells normal and is properly stored.
- Floats to the top: The egg is old. Its air cell has grown large. It may still be safe, but quality has declined and the yolk and white are thinner.
The float test measures age, not bacterial safety. That distinction is the part most people miss. An egg floats because of air, and air has nothing to do with whether Salmonella or another pathogen is present.
Can a Floating Egg Still Be Safe to Eat?
A floating egg can be safe, but it deserves more caution than a sinking one.
Floating means the egg is old enough that its air cell has expanded significantly. Old eggs are more likely to have thinner whites, weaker yolks, and off flavors. They are also more likely to have been stored longer or at inconsistent temperatures, which raises the odds of bacterial growth if contamination occurred.
The float test alone cannot clear an egg for eating. Food safety guidance from public health agencies consistently points to smell and appearance as better day-to-day indicators, along with proper storage. A floating egg that smells normal may still be usable for baking or hard boiling, but many food safety sources advise discarding eggs that float, especially if the shell is cracked or the egg smells off.
When in doubt, throw it out. That advice is not dramatic — it reflects the fact that the float test is imperfect.
Why the Float Test Is Not a Safety Test
The float test cannot detect bacteria. This is the most important limitation, and it is well documented.
Salmonella can be present in or on an egg without changing its buoyancy. Contamination can happen through a cracked shell, through contact with contaminated surfaces, or — in some cases — before the egg is laid. A perfectly fresh egg that sinks can still carry bacteria. A floating egg that is old is not automatically contaminated, either.
There is another wrinkle worth knowing. An egg with a cracked shell can take on water and actually sink even when it is old, or it can leak and behave unpredictably in water. The float test assumes an intact shell.
Because of these limits, the float test is best treated as a rough freshness clue — a starting point, not a verdict.
How Should You Store Eggs to Keep Them Fresh Longer?
Cool, consistent refrigeration is the most reliable way to slow the growth of the air cell and reduce bacterial risk.
In the United States, commercially sold eggs are typically washed and refrigerated, and food safety guidance recommends keeping them refrigerated at home. Storage practices differ in other countries, where eggs are sometimes sold unwashed and stored at room temperature. The key principle is consistency: avoid leaving eggs at warm room temperature for long periods, and avoid repeated temperature swings.
Practical storage points:
- Keep eggs in the refrigerator, ideally in their original carton.
- Store them away from strong-smelling foods, since the porous shell can absorb odors.
- Keep the pointed end down if you can, which helps keep the yolk centered and slows air cell growth.
- Do not wash eggs at home before storing — washing can remove the protective coating and increase the chance of contamination entering through the shell.
Refrigeration slows moisture loss and limits bacterial growth. It does not stop aging entirely, which is why even refrigerated eggs eventually float.
What Other Signs Show an Egg Is Fresh or Spoiled?
Smell is the most reliable everyday signal. A spoiled egg has a distinct, unpleasant sulfur-like odor that is hard to miss once you crack it.
Other signs worth checking:
- The shell: A fresh egg has a clean, uncracked shell. Cracks let bacteria in.
- The white: A fresh egg has a thick, firm white that stays close to the yolk. An old egg has a thin, watery white that spreads out.
- The yolk: A fresh yolk is round and stands up. An old yolk flattens and breaks easily.
- The candling test: Holding an egg against a bright light shows the size of the air cell. A small air cell means a fresher egg. This is a professional grading method, not something most home cooks need.
None of these signs is perfect on its own. Together, they give a much clearer picture than the float test alone.
The Bottom Line on the Float Test
The float test is simple, quick, and based on real physics. It tells you roughly how old an egg is by showing how much its air cell has grown.
But it is not a safety test. It cannot tell you whether an egg is contaminated, and it cannot guarantee a floating egg is safe or that a sinking egg is clean. Use it as one clue among several — smell, appearance, shell condition, and proper storage — and when an egg looks or smells wrong, discard it.
Frequently Asked Questions
Do good eggs float or sink?
Good, fresh eggs sink and lie flat on their side in water. Floating means the egg is older and has a larger air cell, not that it is necessarily spoiled.
Can you eat an egg that floats?
A floating egg may still be safe, but it is older and should be checked for smell and cracks before use. Many food safety sources advise discarding eggs that float, especially if they smell off.
Why do old eggs float?
As an egg ages, moisture escapes through the porous shell and the air cell at the wide end grows larger. More air makes the egg more buoyant, so it floats.
Does a sinking egg mean it is safe to eat?
No. A sinking egg is likely fresh, but the float test cannot detect bacteria like Salmonella. Always check for cracks, smell, and proper storage before eating.
