For many home cooks, a carton of eggs in the fridge can pose a dilemma after a certain amount of time has passed. While the 'sell by' date is a retail guideline, not a hard expiration date, relying on your senses and some simple tests is the most reliable way to determine egg safety.
The float test: A simple and reliable method
The float test is a classic and easy way to gauge an egg's freshness without cracking it open. This method relies on the principle that an egg's shell is porous, allowing air to seep in over time. As an egg ages, it loses moisture and takes in more air, which increases the size of its internal air cell and makes it more buoyant.
To perform the float test:
- Fill a bowl or glass with enough cold tap water to fully submerge an egg.
- Gently place the egg into the water.
- Observe its behavior. If it sinks and lays flat on its side, it is very fresh. If it sinks but stands upright on one end, it is older but likely still safe to eat, best for baking or hard-boiling. If it floats to the surface, the air cell is very large, indicating it is old and should be discarded.
Important nuance: While floating suggests an older egg, it doesn't always mean it is spoiled. The decisive factor is the smell, but if an egg floats, exercising caution and performing the next tests is wise.
Visual and auditory inspection
Beyond the float test, your eyes and ears offer important clues to an egg's condition. Both the shell and the internal contents can reveal if an egg has turned.
Checking the shell
- Appearance: Look for any cracks, sliminess, or powdery residue. Cracks can allow bacteria to enter, while a slimy feel indicates bacterial growth. Powdery spots might be mold. Any of these are strong signs to discard the egg.
- Candling: Using a bright light in a darkened room, you can see the internal air cell. Hold the egg up to the light. The smaller the air cell (located at the wider end), the fresher the egg. A larger air cell indicates an older egg.
After cracking the egg
- Yolk and White: Crack the egg onto a flat plate. A fresh egg will have a firm, round yolk that stands up, surrounded by a thick, slightly cloudy egg white. An older egg will have a flatter yolk and a thin, watery, translucent egg white that spreads out easily.
- Discoloration: Any strange colors, such as pink, green, or iridescent whites, are a definite sign of bacterial contamination, and the egg must be thrown out. Black or green spots within the egg also indicate fungal or bacterial growth.
The ultimate decider: The sniff test
Even if an egg passes the visual checks, the sniff test is the most foolproof method for determining spoilage. A bad egg will emit an unmistakable, pungent, sulfurous odor.
Best practice for the sniff test:
- Always crack eggs into a separate bowl one at a time, especially if you're adding them to other ingredients. This prevents a single rotten egg from ruining your entire dish.
- A fresh egg should have a neutral or mild aroma. If you smell anything sour or sulfurous, throw the egg away immediately. This foul smell is due to hydrogen sulfide gas produced as the egg decomposes.
Older egg characteristics vs. spoilage
Not all signs of age mean an egg is spoiled. It's important to distinguish between an older, but still usable, egg and one that has gone bad.
| Characteristic | Fresh Egg | Older Egg (Not Spoiled) |
|---|---|---|
| Float Test | Sinks and lies flat on its side. | Sinks but stands upright. |
| Shell | Clean, smooth, and intact. | Intact, but may have a slightly more brittle shell. |
| Smell | Neutral or no smell. | Neutral smell (if not spoiled). |
| White (Albumen) | Thick, cloudy, and holds its shape tightly around the yolk. | Thinner, runnier, and more translucent; spreads out easily. |
| Yolk | Round and firm. | Flatter and more easily broken. |
Conclusion
Determining whether eggs have gone off is a multi-step process that utilizes your senses and a simple float test. While the 'sell by' date provides a useful guideline, it's not the final word on freshness. The combination of the float test, visual inspection of the shell and contents, and most importantly, the sniff test, provides a reliable way to ensure you are cooking with safe, healthy ingredients. When in doubt, it is always safest to discard the egg to avoid the risk of foodborne illness. By following these simple steps, you can confidently check the freshness of your eggs and reduce food waste.
