You can tell if a duck egg is bad using a few simple checks: the float test in water, a visual inspection of the shell and contents, and the unmistakable smell of a spoiled egg. Duck eggs have thicker shells than chicken eggs, which gives them a longer shelf life, but they still degrade over time and can harbor bacteria if stored improperly. Here’s how to evaluate them before cooking.
The Float Test
Fill a bowl or glass with cool water and gently place the duck egg in it. A fresh egg sinks to the bottom and lies on its side. As an egg ages, moisture escapes through tiny pores in the shell and is replaced by air, causing the air cell inside to grow larger. An egg that’s a few weeks old will sink but tilt upward or stand on one end. An egg that floats to the surface is old enough that the air cell has expanded significantly, and you should discard it.
The float test tells you about age, not necessarily contamination. An egg that sinks could still be spoiled if it was exposed to bacteria through a cracked shell. And an egg that tilts slightly may still be perfectly fine to eat. Use this as a first screening step, not the final word.
Check the Shell
Before cracking the egg, examine the shell closely. A healthy duck egg shell feels dry and slightly chalky. If the shell feels slimy, that’s a sign of bacterial growth on the surface. A powdery coating that wasn’t there before (distinct from the natural bloom) can indicate mold. Any visible cracks, no matter how small, give bacteria a direct path inside. Discard eggs with cracked or slimy shells without bothering to open them.
Crack It and Look
If the shell passes inspection, crack the egg onto a clean white plate or into a white bowl. The color contrast makes it easier to spot problems. A fresh duck egg has a yolk that sits up tall and rounded, with the white clinging to it in a thick, gel-like layer surrounded by a thinner watery layer. As the egg ages, the yolk flattens out and the white becomes uniformly runny, losing that distinct two-layer structure.
Look specifically for pink, green, or iridescent discoloration in the yolk or whites. These color shifts indicate bacterial growth and mean the egg is unsafe to eat. If you see any discoloration, throw the egg out and wash the plate or bowl with hot, soapy water before testing another egg. A blood spot on the yolk, by contrast, is harmless and doesn’t mean the egg is bad.
The Smell Test
This is the most reliable check. A fresh egg has virtually no smell at all. A bad egg produces a strong sulfur odor that’s impossible to miss, whether raw or cooked. If you crack an egg and catch even a hint of an off smell, don’t use it. There’s no ambiguity with this one: a spoiled egg smells unmistakably rotten.
Candling for Uncracked Eggs
Candling means holding a bright light against the egg in a dark room to see what’s inside. You can use a strong flashlight or a dedicated egg candling light pressed against the wider end of the egg. In a fresh, unfertilized eating egg, you should see a small air cell at the wide end and the yolk as a faint shadow. The contents should look relatively clear and uniform.
A bad egg will appear unusually dark or murky inside. If the yolk’s shadow doesn’t move when you gently tilt the egg, it may have stuck to the shell membrane, a sign of significant degradation. A very large air cell suggests the egg is old. If you’re checking fertilized eggs for incubation rather than eating, look for clear, distinct veins as a sign of a living embryo. Blurry vessels or a yellowish tone instead of vibrant reds and oranges indicates the embryo has died.
How Long Duck Eggs Last
Duck eggs stored in the refrigerator (around 7°C or 45°F) maintain good quality for at least 8 weeks when washed before storage. Unwashed duck eggs kept at room temperature (around 25°C or 77°F) remain at an acceptable, though lower, quality for about 7 weeks. Refrigeration is clearly the better option for both safety and freshness.
There’s a tradeoff with washing, though. Duck eggs naturally have a protective coating called the bloom (or cuticle) that seals the shell’s pores and slows moisture loss and bacterial entry. Washing removes this coating and can even cause small scratches visible under magnification, which shortens shelf life if the egg is then left unrefrigerated. The best approach is to wash duck eggs and refrigerate them immediately. If you have unwashed eggs from your own ducks and plan to use them within a week or two, you can store them at room temperature with the bloom intact, but refrigeration is safer for longer storage.
Why Handling Matters More With Duck Eggs
Duck eggs can carry a higher bacterial load than chicken eggs. A study testing eggs from a traditional market in Indonesia found Salmonella present in duck egg samples but not in the chicken eggs tested alongside them. Ducks tend to lay eggs in wetter, dirtier environments than chickens, which increases surface contamination. This doesn’t mean every duck egg is risky, but it does mean proper storage and thorough cooking matter.
Always cook duck eggs fully rather than eating them runny or raw. Refrigerate them promptly after purchase or collection. If you’re buying from a farm stand or market, choose eggs that look clean and have intact shells. The combination of refrigeration, clean handling, and full cooking eliminates the vast majority of food safety risk, even if an egg has surface bacteria when you first bring it home.