How Reliable Is the Egg Float Test for Determining Safety?

October 25, 2025 •

4 min read

According to the U.S. Department of Agriculture, eggs can be safe to eat for several weeks past the "sell-by" date if stored properly. This fact challenges the popular wisdom of the egg float test, which is often used incorrectly to determine if an egg has gone bad.

Quick Summary

The egg float test indicates an egg's age based on its air cell size, not its safety. More reliable spoilage indicators are smell and appearance.

Key Points

Age Indicator, Not Safety: The egg float test measures an egg's age based on air cell size, not bacterial contamination.
Senses Are Best: A foul, sulfurous smell is the most reliable sign of a spoiled egg.
Visual Inspection is Key: When cracked, a thick egg white and firm yolk indicate freshness, while a watery white and flat yolk suggest age or spoilage.
Proper Storage Matters: Store eggs in their carton on a cool refrigerator shelf to maximize freshness and safety, not the door.
Avoid Food Waste: Don't automatically throw out an older, floating egg; rely on your senses to determine if it's safe to eat.

The egg float test is a time-honored kitchen hack passed down through generations. The premise is simple: place an egg in a bowl of water, and its buoyancy reveals its freshness. While this method can indicate an egg's age, it is widely misunderstood and not a foolproof measure of food safety. Relying solely on it can lead to unnecessary food waste or, more seriously, consuming an egg that poses a health risk.

The Science Behind the Egg Float Test

To understand why the float test works, it's necessary to look at an egg's structure. An eggshell, despite its appearance, is porous. Inside the egg, at its larger end, is a small air cell.

As an egg ages, two key things happen:

Moisture Loss: The egg's internal moisture evaporates through the porous shell over time.
Air Expansion: As moisture leaves, the air cell inside the egg expands to take its place. A larger air cell makes the egg more buoyant.

This is why a very fresh egg, with a small air cell and a higher density, will sink and lie flat at the bottom of a bowl of water. An older egg with a larger air cell will stand on its end or eventually float.

Why the Test Isn't Reliable for Safety

The major flaw with the egg float test is that it correlates age with spoilage, which is not always accurate. While a very old egg is more likely to be spoiled, its age doesn't guarantee it. Conversely, a fresh-sinking egg could still be contaminated with bacteria like Salmonella, a risk not visible on the surface. Bacterial contamination can happen during or after laying and doesn't affect the air cell size in the same way as age.

Comparing the Float Test with Reliable Indicators


Indicator	What It Shows	Reliability for Safety	Best Uses
The Float Test	Age only: Based on air cell size.	Unreliable: Indicates age, not whether bacteria is present.	Hard-boiling (older eggs peel easier), baking (older whites whip better).
The Sniff Test	Spoilage: Foul, sulfurous odor.	Highly Reliable: A strong odor is a clear sign of spoilage.	Confirms if a floating egg is truly rotten.
The Visual Test (Cracked)	Quality: Firm, round yolk and thick egg white.	Reliable: Watery white, flat yolk, or pink/green coloration indicate reduced quality or spoilage.	Best for determining egg quality for specific dishes like poaching or frying.
The Shake Test	Staleness: A sloshing sound.	Moderately Reliable: Indicates a watery consistency, a sign of age, but not definite spoilage.	Quick, non-invasive check for egg whites needed for baking.

More Reliable Methods for Testing Eggs

Instead of relying on the float test for safety, use your senses, particularly the sniff test and visual inspection.

The Sniff Test: A rotten egg will produce an unmistakable, sulfurous odor. This is the single most reliable test for spoilage. If you're in doubt, crack the egg into a separate bowl to avoid contaminating other ingredients or surfaces.
The Visual Test: Crack the egg onto a plate. A fresh egg will have a plump, rounded yolk and a thick, compact white that doesn't spread much. An older egg will have a flatter yolk and a thin, watery white that spreads out. Discoloration like pink or green spots in the white or black spots on the yolk are clear signs of bacteria and should be discarded.
The Shake Test: Hold the egg to your ear and shake it gently. If you hear a significant sloshing sound, it indicates that the contents have thinned and the egg is older. This is a decent indicator of age but, again, not spoilage.

Proper Egg Storage and Food Safety

The most effective way to prevent spoilage and maintain egg quality is proper storage. Most grocery store eggs in the U.S. have been washed, which removes the protective cuticle, so they must be refrigerated.

Store eggs in their original carton on a shelf inside the refrigerator, not the door. The temperature on the door fluctuates more, which can speed up aging.
Keep eggs away from strong-smelling foods, as their porous shells can absorb odors.
Always cook eggs thoroughly, especially for young children, the elderly, or those with weakened immune systems, to kill any potential bacteria.

For more information on proper egg handling and safety, refer to guidelines from the USDA.

Conclusion: Age vs. Safety

In conclusion, the egg float test is not reliable for determining food safety. While it can accurately indicate an egg's age by measuring the growth of its internal air cell, age is not synonymous with spoilage. Floating eggs might simply be older but still perfectly good for baking or hard-boiling, while a sunken egg could still carry bacteria. To ensure safety, trust your senses and discard any egg that has a foul smell or appears discolored or watery upon cracking. Correctly evaluating egg quality helps reduce food waste and keeps your diet safe and healthy.

Visit the USDA website for additional resources on food safety and handling.

Frequently Asked Questions

A floating egg is older and has a larger air cell, but it is not necessarily spoiled. While it may not be ideal for poaching or frying, it can still be perfectly safe to eat if it passes the sniff test upon cracking and has no off-putting visual cues.

If an egg stands on its end but remains submerged, it is older than a fresh egg that lies flat but is still likely safe to eat. The larger air cell causes it to stand upright, and it's ideal for hard-boiling because the older membrane makes peeling easier.

No, the egg float test is not foolproof for identifying bad eggs because it indicates age, not bacterial contamination. An egg can float and be fine, or sink and be contaminated. The sniff test is much more reliable.

The most accurate method is the sniff test. Crack the egg into a separate bowl. If it emits a foul, sulfurous smell, it is rotten and should be discarded immediately.

The 'best by' date on an egg carton indicates when the egg is at peak quality for flavor. It is not an expiration date, and eggs can often be safely consumed several weeks beyond this date if they have been stored properly.

The test works for both, but the speed of air cell growth depends on storage conditions. Unrefrigerated eggs will age faster, causing them to float sooner than refrigerated ones. Always use cold water for the test.

To keep eggs fresh, store them in their original carton on a middle or lower shelf inside your refrigerator. This placement provides a more stable and consistently cold temperature than the door.