A floating egg indicates age, not spoilage. Eggs sink when fresh and float when older due to air pocket expansion. This test assesses age, not safety.
The float test relies on changes in internal density. Fresh eggs have tightly packed albumen and a small air cell. As eggs age, moisture evaporates through pores in the shell, increasing the size of the air cell. This reduces density, causing the egg to rise. A floating egg isn't automatically bad-it's simply older.
According to the USDA, eggs remain safe to eat for 3-5 weeks past the pack date if refrigerated. The float test doesn't replace expiration dates or proper storage. An egg may float yet still be perfectly edible.
Place a raw egg in a bowl of cold water. If it sinks and lies flat on the bottom, it's very fresh. If it stands upright on the bottom, it's a few days old. If it floats, it's at least a week old, possibly longer.
This process takes 24-48 hours. A newly laid egg has a density close to water. Over time, the air cell grows from ~0.2 mL to over 1 mL. Once the air cell exceeds 1 mL, the egg typically floats.
For context, a study published in the Journal of Food Science found that eggs stored at 4°C (39°F) retained quality for up to 42 days. Floating occurred in 60% of samples after 28 days, but none were spoiled. The test measures age, not microbial risk.
Eggs consist of shell, membrane, albumen (white), yolk, and air cell. The shell is porous-about 7,000 pores per egg-allowing gas exchange. Oxygen diffuses out, nitrogen and carbon dioxide diffuse in during aging.
As the air cell expands, buoyancy increases. The egg's center of gravity shifts. A floating egg often wobbles or spins slowly due to uneven mass distribution. This motion is normal and not a sign of contamination.
When an egg floats, the albumen becomes thinner and less viscous. The yolk may appear flatter and more fragile. These changes don't affect safety but do impact cooking performance-poached eggs may not hold shape well.
Many assume a floating egg is rotten. That's false. A floating egg can be safe, nutritious, and suitable for baking or scrambling. The USDA confirms that properly stored eggs remain safe beyond their sell-by date.
Another error is testing eggs at room temperature. Cold eggs float more easily because water density increases slightly when chilled. Always use cold tap water and refrigerated eggs for accurate results.
Some people crack floating eggs into a separate bowl to check for smell or texture. While this works, it's unnecessary. The float test is a screening tool, not a substitute for visual or olfactory inspection. If an egg smells sour or the whites appear discolored, discard it regardless of float behavior.
Use floating eggs in recipes where texture isn't critical. Baking, scrambled eggs, omelets, and custards work well. The increased air cell improves leavening in cakes and muffins.
For hard-boiling, floating eggs may crack more easily due to internal pressure. Reduce heat and simmer gently. A 10-minute boil with a cold-water shock yields firm whites and intact yolks.
Here's a real-world example: I tested 12 eggs from a carton labeled "Best By: May 15." Five floated. I boiled two, baked a cake with four, and scrambled three. All performed normally. None had off odors or textures. The float test flagged age-but not failure.
| Float Result | Estimated Age | Safety Status | Best Use |
|---|---|---|---|
| Sinks flat | 0-3 days | Safe | Raw consumption, poaching |
| Stands upright | 4-7 days | Safe | Baking, scrambled eggs |
| Floats | 8+ days | Safe if stored properly | Cake batter, soufflés, custard |
Confusion arises because floating suggests "bad" in everyday language. But in science, float = low density, not decay. A ship floats because it displaces water equal to its weight. An egg floats for the same reason.
Also, many people don't know eggs are graded by USDA standards. Grade AA eggs have thick whites and high, round yolks. As they age, they lose structure. The float test detects this loss-but not bacterial growth.
Salmonella risk depends on handling, not float status. The CDC reports that 1 in 20,000 eggs carry Salmonella. Refrigeration reduces risk by 90%. A floating egg is no more likely to harbor pathogens than a sinking one.
Store eggs in the coldest part of the fridge-not the door. Door shelves fluctuate between 4°C and 10°C, accelerating evaporation. The ideal spot is the middle shelf, where temperature stays stable.
Keep eggs in their original carton. The cardboard reduces moisture loss and prevents odor absorption. A study in Food Chemistry showed that eggs stored in cartons lost 15% less moisture over 30 days compared to loose storage.
Never wash eggs before storing. Water forces through shell pores, increasing internal moisture loss. Wash only before use. The USDA advises against washing unless necessary.
They're neither good nor bad-just older. A floating egg is not unsafe, but it's less ideal for raw consumption or delicate preparations. Use it in cooked dishes where freshness matters less.
If you're unsure, crack the egg into a bowl. Check for clarity, color, and smell. A bad egg has a sulfurous odor and thin, runny whites. A floating egg with normal appearance is fine.