The egg float test tells you something about an egg’s age, not whether it is free from harmful bacteria. Eggs tend to become more buoyant as they lose moisture and the air space inside grows. A floating egg is often older or lower-quality, but it is not automatically rotten. A sinking egg may still be contaminated if it has been stored or handled unsafely.
Why does an older egg rise in water?
An eggshell has thousands of tiny pores. Over time, moisture and carbon dioxide escape, and the air cell near the wider end expands. A sufficiently large air cell lowers the egg’s overall density so it can stand at an angle or float. This change is about age and internal gas space; it is not a laboratory safety test.
The USDA Food Safety and Inspection Service says a floating egg has an enlarged air cell and may be poor in quality, yet can still be safe.
How to read the three common positions
- Lies flat at the bottom: generally a newer egg with a relatively small air space.
- Stands on end while submerged: often a somewhat older egg with a larger air cell.
- Floats at the surface: likely an older egg, although the result alone cannot determine spoilage or microbial safety.
The proportions of dissolved salt in water, shell characteristics and other variables can affect buoyancy too. Use plain water if you are simply curious about egg age, and do not use floating or sinking as permission to ignore storage guidelines.
Can a bad egg sink?
Yes. Salmonella and some other harmful bacteria are not reliably detectable by a float test, smell, or appearance. Even a fresh-looking egg should be refrigerated appropriately, protected from cross-contamination, and cooked safely. Discard eggs with obvious cracks or signs of leakage unless you are following a specific food-safety procedure for handling them.
Utah State University Extension emphasizes that the float test does not establish food safety; a normal smell cannot guarantee the absence of pathogens either.
What should you do with an egg you are unsure about?
Check how the eggs were stored and their use-by guidance. Crack a questionable but properly refrigerated egg into a separate small bowl rather than directly into your recipe. Throw it away if it smells off or looks unusual. Do not taste a suspicious egg. If storage history is unknown or it was left unrefrigerated beyond safe limits, discard rather than gambling on the float test.
For people more vulnerable to foodborne illness—including young children, older adults and those with weakened immune systems—use pasteurized products where a recipe requires undercooked eggs, or fully cook the eggs. Thorough cooking and refrigeration are far more useful safeguards than a glass of water.
FAQ
Does adding salt to the water improve the test? No. Salt increases water density and can make an egg float regardless of its age, making the result less useful.
Does an egg that floats have to be thrown away? Floating alone does not prove spoilage, but if you are uncertain about storage or see anything abnormal, throwing it out is a sensible precaution.
How can I check the carton date? See our guide to reading egg carton dates.
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