There are two simple ways to test how fresh your eggs are. One requires cracking the egg, and one doesn't.
The simplest way to test for egg freshness is to submerge it in a container of water.
- A very fresh egg will lie flat on the bottom.
- An egg that's about a week old will be slightly buoyant, so it will rise up from the bottom of the water just a little.
- By three weeks old, an egg will stand straight up in the water.
The reason this test works is that every egg has a thin membrane inside which forms a small air pocket. As the egg ages, the air pocket expands, and as it expands, the egg becomes more buoyant.
This test is useful if you're making hard boiled eggs, because when the air pocket expands, it makes the egg easier to peel. Thus, the best eggs for making hard boiled eggs are at least a week old. If they stand at least halfway up in the water, they should be fine.
Note that if the egg floats all the way to the surface of the water, it's really old and you should just toss it.
There's another way to test the freshness of an egg, but you need to crack the egg onto a plate or some other flat surface.
- A freshly laid egg will be firm, tall and compact, with the yolk toward the center.
- A week-old egg will have a looser, thinner white, and the yolk will slide toward the edge.
- After three weeks, the yolk will be quite flat and the white will be very thin and runny.
Also see: How to Separate Eggs