If you're wondering about how fresh your eggs are, it's easy enough to look at the date on the carton. But that date is meaningless without some way to interpret that date. Is a week old tool old? How about a month? And more importantly, does egg freshness even matter?
Let's look at what happens when an egg ages.
First of all, egg shells are porous. This means that if you have something with a strong odor in your fridge, your eggs are capable of absorbing that odor over time.
The pH level of an egg white increases (becomes more alkaline) as it ages, and if you're using those egg whites to make a meringue, two things will happen. Firstly, older eggs will foam up more quickly and with less beating than fresh eggs. But that foam will collapse more easily than one made from fresh egg whites, which take longer to whip but end up producing a more stable foam.
Pastry chefs swear that older eggs are easier to incorporate into cake batters, since the older they are, the less firm they are. This slightly more runny consistency means they blend in more easily with the milk, flour and other ingredients.
Moreover, it's well-known that making hard-boiled eggs using older eggs will yield eggs that are much easier to peel.
On the other hand, if you're serving eggs for breakfast, particularly fried eggs, over-easy or sunny-side up eggs, fresh eggs will definitely look better. The yolks will be firmer and stand taller, and be more centered. And fresh eggs will certainly have a superior flavor.
But how can you tell the difference between a fresh egg and a not-so-fresh one?
There are two simple ways to test how fresh your eggs are. One requires cracking the egg, and one doesn't.
Testing Your Eggs for Freshness
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.