The theory is that, as an egg ages, the air pocket inside it grows larger, buoying an old egg to the surface. But, according to Dr. Schaffner, “there is no scientific basis for the egg float test.” So experimenting to see if your egg sinks or swims is not a reliable way to measure its quality.
The water test for egg freshness
First, fill a bowl or glass with about four inches of cold water and gently place your egg(s) inside. Very fresh eggs will sink to the bottom and lay on their sides. If an egg stays at the bottom but stands on its small end, it's still acceptable to eat; just not quite as fresh.
Float test
While it does not determine whether an egg has gone bad, it provides a useful indication of the age of an egg. To perform the float test, place the egg in a large bowl of water. If it sinks or stays at the bottom, it is still fresh. An older egg will either stand on its end or float.
If the eggs sink to the bottom and lay flat on their side, they're still fresh. However, if they sink, but stand on one end at the bottom of the glass or bowl, they're not as fresh but still edible. Of course, if any eggs float to the top, they shouldn't be eaten.
In short, you can eat eggs two months out of date. It'll be fine. If you eat an outright bad egg, that's a different story. Eggs pretty exclusively spoil from contamination, and the signs and symptoms are pretty clear if you consume an egg that's been harboring salmonella.
If an egg sinks to the bottom of a bowl of water and lies sideways, it is very fresh; if it stands on one end in bottom of the bowl, it is less fresh but still good to eat. But if it floats to the surface of the water, indicating that air has permeated the shell, it is no longer fresh.
As long are they are kept refrigerated at 45 °F or lower, fresh shell eggs are safe to be consumed four to five weeks beyond the carton's Julian date (the date eggs were packed).
How It Works: The egg is denser than the fresh water (more molecules per square inch), this causes it to sink. When you start dissolving salt in the water, this is increasing the density (adding more molecules per square inch). Eventually the water becomes denser than the egg causing the egg to float.
To conduct a float test, fill a bowl or cup with water (it should be big enough to fully submerge your egg). Gently place your egg inside and see if it sinks or floats. If it floats, it's old and you may want to toss it.
The best way to test if your eggs are still good after you've boiled them is, again, the smell test. Basically, you'll notice the smell is off if an egg is starting to go bad. This is true for raw eggs and it's true for boiled eggs—the funk doesn't lie.
Saltwater is denser than fresh water because of its salt content. The egg will sink in the fresh water because it has greater density than the water. The egg will float in the salt water because when salt is added to water its density becomes greater than that of the egg.
The inside of the egg is mostly, but not all water (about 90% water). When you put the egg into pure water, some of the water molecules from the solution move into the egg and the egg swells up. You can tell this happens easily if you use food coloring because the egg will change color.
The density of the average egg will be slightly greater than that of water, so it will sink. To make the egg float, we have to make the water more dense by adding salt. For 1 cup of water, adding 3 tbsp. of salt should be about enough to make the egg float.
What happens if you use old eggs. If you use older eggs, the cakes will not rise as well and pavlovas will be flatter than they should be. Generally, the cakes will still work as long as you get some volume from beating, they just won't be as tall or light-as-air as they should be.
“As long as the egg hasn't gone bad, there's no reason you can't still enjoy it,” says nutritionist Keri Gans, RD, author of The Small Change Diet. That's right: You do not have to trash that carton of eggs just because it's past the sell-by date. You'll save money and eliminate food waste.
Because of their numerous benefits, it's OK to eat one whole egg, including the egg yolk, every day if you don't have cardiovascular disease and you do have a healthy level of blood cholesterol.
If they sink to the bottom and lay flat on one side, they are fresh and good to eat. A bad egg will float because of the large air cell that forms at its base. Any floating eggs should be thrown out.
Eggs may be refrigerated three to five weeks from the day they are placed in the refrigerator. The "Sell-By" date will usually expire during that length of time, but the eggs will be perfectly safe to use. Always purchase eggs before the "Sell-By" or EXP (expiration) date on the carton.
Anyway, as the egg gets older it ends up with more gas inside and less water, and the gas is lighter than the water. Overall, this makes the egg lighter and in fact less dense than water so that a stale egg floats.
According to the USDA Food Safety and Inspection Service (FSIS), you can freeze eggs for up to one year. When you're ready to use frozen eggs, thaw them overnight in the refrigerator or under running cold water. Use egg yolks or whole eggs as soon as they're thawed.
If the egg lies horizontally, it's at its freshest. If the narrow end of the egg tilts upward, the egg is still usable, but not quite as fresh. An egg that tilts would be good to use for meringue (yes, older eggs do make better meringue!).
Bring to a boil, then cover the pot and turn off the heat. Let the eggs cook, covered, for 9 to 12 minutes, depending on your desired done-ness (see photo). Transfer the eggs to a bowl of ice water and chill for 14 minutes. This makes the eggs easier to peel.