How do you know when eggs are not safe to eat?: A Guide for Your Nutrition Diet

October 7, 2025 •

5 min read

According to the U.S. Food and Drug Administration (FDA), raw or undercooked eggs can contain Salmonella, a harmful bacterium that causes foodborne illness. This makes knowing how do you know when eggs are not safe to eat? an essential skill for anyone serious about their nutrition diet and overall health.

Quick Summary

Learning to recognize signs of egg spoilage is crucial for food safety. Simple tests involving smell, visual inspection, and water buoyancy can help determine if eggs are fresh enough for consumption. Proper storage is also key to preventing bacterial contamination and preserving quality.

Key Points

The Float Test: A fresh egg sinks and lies flat in water, while an older egg will stand on end or float, indicating an enlarged air cell.
The Sniff Test is Reliable: A fresh egg has no odor; a rotten egg will emit a distinct sulfurous, foul smell, and should be discarded immediately.
Visual Inspection of the Shell: Look for cracks, sliminess, or a powdery substance, as these can indicate bacterial or mold contamination and mean the egg is unsafe.
Inspect the Interior: Crack the egg into a bowl and check for discoloration (pink/green/iridescent), a flat yolk, or watery white, which are all signs of spoilage or old age.
Store Eggs Properly: Refrigerate eggs in their original carton in the main part of the fridge to maintain a consistent cold temperature and prevent bacterial growth.

Eggs are a nutritional powerhouse, packed with protein, vitamins, and minerals, making them a staple in a balanced diet. However, like any perishable food, they have a limited shelf life and can pose a health risk if consumed after they have gone bad. Recognizing the signs of spoilage is critical for preventing foodborne illnesses, such as those caused by Salmonella. This comprehensive guide will equip you with the knowledge to inspect your eggs with confidence.

The Crucial Checks: Float, Smell, and Visual Inspection

Determining an egg's safety doesn't require a laboratory. You can perform several easy and reliable tests right in your kitchen. Combining these methods offers the best chance of catching a potentially spoiled egg before it becomes a problem.

The Water Float Test

This simple, popular method assesses an egg's freshness by measuring the size of its air cell. As an egg ages, its shell becomes more porous, allowing moisture to escape and air to enter, which causes the internal air cell to enlarge.

How to perform the test: Place the raw egg in a bowl of water. If it sinks and lies flat on its side, it is very fresh. If it sinks but stands on its pointed end, it is older but likely still safe to eat. If the egg floats, it is quite old and should be used with caution, if at all. A floating egg has a large air cell, indicating significant age, and should be further tested with a sniff and visual check.

The Sniff Test

Your nose is one of the most reliable tools for detecting spoiled food, and eggs are no exception. Spoiled eggs release an unmistakable, foul, sulfur-like odor caused by the production of hydrogen sulfide gas from bacteria.

How to perform the test: If you are unsure about an egg's freshness, crack it into a clean bowl before adding it to other ingredients. If it smells bad, throw it out immediately and wash the bowl with hot, soapy water. A fresh egg should have little to no scent.

The Visual Inspection

Checking the egg's appearance, both inside and out, can reveal important clues about its condition.

Shell Inspection: Check the shell for any cracks, sliminess, or a powdery residue. A cracked shell compromises the egg's protective barrier, allowing bacteria to enter. A slimy or powdery coating can indicate bacterial or mold growth on the surface. If you see any of these signs, discard the egg.
Internal Inspection: Crack the egg onto a clean, white plate to check the color and consistency of the yolk and white. Look for any unusual discoloration, such as pink, green, or iridescent hues in the white, which can signal bacterial spoilage. The yolk of a fresh egg should be firm and rounded, and the white should be thick and viscous, holding its shape tightly around the yolk. A runny, watery white or a flattened, easily-broken yolk indicates an older, lower-quality egg, though it may not be unsafe if it passes the sniff test.

Proper Storage and Handling for Prevention

Preventing spoilage starts with proper handling from the moment of purchase.

Refrigerate Immediately: Always buy eggs from a refrigerated section and store them in the refrigerator as soon as you get home. Keeping them in the main part of the fridge, rather than the door, ensures a consistent, cold temperature (below 40°F/4°C), which inhibits bacterial growth.
Keep in the Carton: The original carton helps protect the eggs from absorbing strong odors from other foods and provides an extra layer of protection against contamination. It also keeps the sell-by date visible.
Handle with Care: Always wash your hands and any surfaces or utensils that have come into contact with raw eggs to prevent cross-contamination.

Comparison of Fresh vs. Spoiled Eggs


Characteristic	Fresh Egg	Spoiled Egg
Float Test	Sinks and lies flat at the bottom.	Tilts upwards or floats.
Odor	Neutral or no smell.	Strong, sulfur-like, foul smell.
Shell Appearance	Clean, dry, and intact.	Cracked, slimy, or powdery residue.
Yolk Appearance	Rounded, firm, and centrally located.	Flat, spreads easily, or discolored.
White Appearance	Thick, viscous, holds its shape.	Runny, watery, spreads out, or shows pink/green/iridescent tint.

Other Indicators of Spoilage

Beyond the primary tests, other signs can point to a decline in egg quality or safety.

Check the Date: While expiration dates are not always a perfect indicator, they offer a good guideline. Eggs are generally safe for several weeks past the pack date if stored properly. However, it's always wise to combine this with other freshness tests.
The Sound Test: Gently shake the egg next to your ear. If you hear a sloshing or rattling sound, it's a sign that the egg is old and the contents have become watery. A fresh egg should have no internal movement.
Candling: Although typically a commercial process, you can perform a basic version at home by holding an egg up to a bright light in a dark room. A fresh egg will have a small air cell, while an older one will have a larger air pocket.

What to Do If You're Still Unsure

If an egg passes all the visual and sniff tests but you still have doubts, it's safest to discard it. When in doubt, throw it out. For foods that require raw or lightly cooked eggs, such as homemade mayonnaise or tiramisu, using pasteurized eggs is a safer alternative, especially for vulnerable individuals like pregnant women, young children, the elderly, or those with compromised immune systems. Proper cooking, which involves heating the egg until the yolk and white are firm, kills most harmful bacteria and makes eggs safe for consumption.

For more detailed information on food safety and egg handling guidelines, you can consult the official U.S. Food and Drug Administration website.

Conclusion

Being proactive about egg safety is a fundamental aspect of maintaining a healthy nutrition diet. By mastering a few simple techniques—the float test, the sniff test, and a thorough visual inspection—you can easily determine the freshness and safety of your eggs. Proper storage, including immediate refrigeration in the original carton, further reduces the risk of contamination. While eggs are a wonderfully nutritious and versatile food, responsible handling and a keen eye for signs of spoilage are essential to enjoying them safely and protecting your health. Never take a risk if an egg appears or smells off, as the consequences of foodborne illness far outweigh the cost of discarding a single spoiled item.

- Authoritative Link: FDA What You Need to Know About Egg Safety
- Authoritative Link: CSIRO Egg quality and safety

Frequently Asked Questions

If an egg passes the float test but has a foul, sulfurous odor when cracked, it should be discarded immediately. The float test indicates age, but the sniff test is the most reliable indicator of spoilage and bacterial contamination.

An egg that floats is older due to a larger air cell but isn't necessarily spoiled. However, for the safest approach, you should crack it into a bowl and perform a sniff and visual test. If there is any doubt, throw it out.

Yes, a green or grayish ring on the yolk of a hard-boiled egg is safe to eat. It is caused by overcooking, which releases iron from the yolk and reacts with sulfur from the white.

With proper refrigeration, eggs are typically safe to eat for 3-5 weeks past the pack date, though the sell-by date might expire sooner. Always rely on freshness tests like smell and appearance to confirm safety rather than just the date.

A slimy or powdery shell is a strong indicator of bacterial or mold contamination and means the egg is not safe to eat. Discard such eggs immediately and wash your hands and any surfaces that came into contact with them.

While cooking thoroughly can kill many harmful bacteria like Salmonella, it is not a foolproof solution for a spoiled egg. The toxins produced by some bacteria may be heat-stable, and the quality and safety are already compromised. If an egg smells or looks bad, do not risk it.

Cracked eggs have a compromised protective barrier, allowing bacteria to enter easily. The general recommendation is to discard cracked eggs to avoid the risk of foodborne illness, as thorough cooking may not eliminate all bacteria.