The dates stamped on the carton only tell you when eggs are at peak freshness; they're fine to eat for longer than that. A true test uses a simple glass of water: Fill a pint glass or mixing bowl halfway with room temperature water and place an egg in it. If the egg stays horizontal at the bottom, it’s very fresh. If it starts to bob and tilt, it’s around 10 days old; if it floats vertically, it’s stale.
Why’s this? Eggs have porous shells. So, over time, the water inside the egg starts to evaporate, and to maintain equilibrium, it takes in air. This isn’t all negative, though. Older eggs (ones that tilt) are actually great for making hard-boiled eggs, because the extra air pocket makes them easier to peel.
2. Center your yolk: A quick fix
It can be frustrating to make a batch of deviled eggs and not know where the yolk will settle when you boil the eggs. When they rest on their sides during cooking, the yolks follow gravity and the whites are pushed aside, leaving thinner areas of white. After peeling and cutting the eggs in half, sometimes you’ll get broken sides of the whites that aren’t strong enough to hold the filling.
To prevent this, molecular gastronomist Hervé This has a very simple solution: Just stir the eggs around in the pot a few times during cooking. A slow centrifugal force will keep the yolk from leaning one way or the other.
3. Get rid of the dreaded green ring
When you make hard-boiled eggs, you’ll sometimes see a green-grey ring around the yolk. It’s harmless, but unsightly. The ring appears in over-cooked eggs when the sulfur in the egg white reacts with the iron from the yolk. It also smells a little funky — like hot springs — because of the sulfur.
One way to avoid the ring is to “shock” the eggs by placing them in a large bowl of ice-cold water immediately after boiling. This will stop the cooking process right away. Another way is to reduce the intense direct heat of boiling by using a gentler cooking method. Steaming or pressure-cooking the eggs are good alternatives. Make sure the eggs are completely shocked and cooled before storing in the refrigerator for up to a week.