You drop an egg into a glass of water and it floats. The internet’s usual verdict is immediate: “bad egg.” But the test does not actually tell you that. Floating mainly tells you the egg is older, because its air cell has grown; it is not a safety test.
The clearest household sign of genuine spoilage usually appears after cracking the egg: a strong, unpleasant odor. Freshness, spoilage and microbiological safety are different questions, and separating them makes the common egg tests much easier to understand.
What the main signs actually mean
| Sign | Meaning |
|---|---|
| Rotten or strongly off odor after cracking | Discard |
| Clearly abnormal appearance | May indicate spoilage |
| Cracked or leaking shell | Higher contamination concern |
| Egg floats in water | Larger air cell and older age |
| Thin, runny white | Lower freshness, not automatically spoilage |
Smell is the most direct spoilage clue
A spoiled egg develops a characteristic unpleasant odor whether raw or cooked. If you are unsure about an older egg, crack it into a small separate bowl before adding it to batter, a skillet or other eggs.
There is no reason to taste it. A clearly bad smell is enough reason to throw it away.
What the float test is really measuring
As an egg ages, moisture and gases escape through the shell and the internal air cell grows. That changes buoyancy.
- Sinks and lies flat: usually fresher.
- Sinks but stands upright: older.
- Floats: has a larger air cell and is older still.
USDA notes that a floating egg can still be usable. The test does not detect Salmonella or other pathogens. The reverse matters too: an egg that sinks is not certified pathogen-free.
A runny white usually tells you about age, not rot
Fresh egg whites tend to be thicker and the yolk sits higher. As the egg ages, the white becomes more fluid and spreads farther in a pan.
That can affect cooking quality — for example, how neatly a fried egg holds together — but it is not automatically a sign of dangerous spoilage.
Yolk color is not a freshness gauge
A deep orange yolk does not prove the egg is fresher, and a pale yolk is not a spoilage sign. Color depends mainly on pigments in the hen’s diet.
Blood spots are usually less dramatic than they look
A small blood spot can result from a tiny ruptured vessel during egg formation. It does not mean the egg is fertilized or rotten and can be removed for appearance if desired.
The shell deserves more attention
An intact shell is a protective barrier. An egg that has been cracked and leaking for an unknown amount of time creates more opportunity for contamination than one you crack immediately before cooking.
Can a normal-smelling egg contain Salmonella?
Yes. Pathogens do not have to produce a detectable odor. Storage, handling and cooking still matter even when the egg looks and smells normal.
Refrigerator storage in the U.S.
USDA recommends refrigerating shell eggs and lists a typical refrigerator storage time of 3–5 weeks from purchase. Hard-cooked eggs keep about 1 week.
A simple way to check an egg you are unsure about
- Check that the shell is intact.
- Crack the egg into a separate small bowl.
- Look for a clearly abnormal appearance.
- If there is a strong off odor, discard it.
- If it appears normal, use it within appropriate storage and cooking practices.
What is worth remembering
Smell after cracking is a spoilage clue; floating is an age clue. An older floating egg may still be usable, and a sinking egg is not guaranteed safe. That distinction keeps a popular kitchen trick useful without asking it to do a job it cannot do.
Sources
- USDA FSIS — Shell Eggs from Farm to Table — Egg freshness, float test and handling.
- FoodSafety.gov — Cold Storage Chart — Refrigerator storage times.