You know that moment — you are halfway through a recipe, butter softened, oven preheated, and the carton of eggs in your fridge has a “best by” date from three weeks ago. Are they still good? You crack one into a bowl and pray it does not smell like sulfur.

There is a better way, and it takes five seconds.

The Float Test: Your Kitchen’s Lie Detector

Fill a bowl or tall glass with cold water. Gently place the egg in. That is it. What it does tells you everything:

• Sinks and lies flat on its side: Very fresh. Use for poaching or frying where you need the yolk to hold its shape.
• Sinks but stands upright on the bottom: Still good, but aging. Use for baking or hard-boiling — the slightly larger air pocket makes them easier to peel.
• Floats to the surface: Toss it. The air pocket has expanded enough to lift the egg, which means decomposition is well underway.

Why does it work? Eggshells are porous. Over time, moisture evaporates through the shell and air seeps in to replace it. More air equals more buoyancy. A fresh egg has almost no air inside. A three-month-old egg is basically a tiny blimp.

The Shake Test (Backup Method)

Hold the egg to your ear and shake it gently. A fresh egg is silent — the contents fill the shell completely. An old egg sloshes. You will hear liquid moving around because the contents have shrunk and separated from the shell.

If you hear sloshing, float-test it to confirm. If it floats, do not crack it — the smell will clear your kitchen.

The Plate Test for Cracked Eggs

If you have already cracked an egg and are unsure, look at the white. A fresh egg white is thick and cloudy — it holds its shape around the yolk. An older egg white spreads thin and watery like it gave up. The yolk of a fresh egg sits tall and domed; an old yolk flattens out.

I float-test every egg now when I am making something where the egg is the star — carbonara, soft-scrambled, poached. The difference between a week-old egg and a month-old one is visible on the plate.