Because eggs stored securely in the refrigerator can stay fresh way beyond the advertised sell-by date, it's helpful to learn ways to identify whether they are still edible or not. Beyond breaking eggs one by one into a bowl, a few signs can help you figure out whether an egg is fresh or rotten.
About Those Dates
According to USDA standards, the expiration date printed on an egg carton can be no longer than 30 days after the eggs were packed, but "use by" or "best before" dates can be no more than 45 dates after packing. Eggs, however, can stay fresh for surprisingly long periods in the refrigerator; they should not stay at room temperature for longer than two hours, however. Likewise, hard-boiled eggs should be refrigerated within two hours of cooking and consumed within a week, because cooking removes the protective coating. Although eggs can occasionally carry salmonella bacteria, do not wash them before cooking, as this can drive the bacteria inside the shell. Whatever the freshness, eggs should be cooked throughout to at least 160 degrees Fahrenheit.
A simple, dependable way to gauge the freshness of a raw egg from the fridge exploits the porous nature of eggshell. A freshly laid egg has a tiny pocket of air at the broader end between the shell and the membrane, which gradually expands as the egg ages. As a result, an egg’s freshness can be identified by dropping it gently into a bowl or glass of cold, unsalted water. If it sinks flat to the bottom, lying sideways, it is extremely fresh. A week-old egg will tilt upward slightly but still touch the bottom. A two-week-old egg stands upright or bobs beneath the surface with the wider end upward, but is still usable. If the egg floats to the surface, however, it is typically more than four to five weeks old and should be discarded. Furthermore, a fresh egg makes no sound when shaken, whereas a bad egg will rattle because of the air pocket inside.
An egg that is too old to use will usually announce itself with a foul, sulfurous odor when cracked. Other indicators are more subtle. Visually, the yolk of a fresh, cracked egg should be bright yellow and mounded, surrounded by a gelatinous ring. Older eggs tend to appear paler and lie flatter. Paradoxically, the albumen of a super-fresh egg is slightly cloudy, but clarifies with age. Although specks of blood in the albumen are not a bellwether of freshness, whites that are tinged pink, green or black can confidently be discarded. Avoid eggs with cracked shells. After it's boiled, the shell of a fresh egg should be difficult to remove, while the shell of an older egg peels away more easily.
The freshness of an egg somewhat dictates its potential use. When appearance and integrity are important, fresh eggs with a bright yolk are best. They separate the easiest in the pan, making them ideal for poaching or frying. The freshest eggs also make the lightest souffles. Medium-fresh eggs, those that tilt slightly in water, are fine for making omelettes, hard-boiling or baking. Even older eggs on the cusp of turning have their uses -- as deviled eggs, where the yolk is mixed with mayonnaise, mustard and relish.