When your chickens are laying well, sometimes you can start to get more eggs than you’re able to use. When you go to use the eggs in your recipes, it’s good to be able to tell which ones are getting old and which ones are still fresh.
Although it’s not obvious to the eye, eggshells are porous. Each egg has thousands of tiny pores in its shell. This allows the egg to “breathe,” letting out carbon dioxide and moisture and taking in air. When you consider that the role of an eggshell to protect and help provide a nurturing environment for a developing baby chick, then it’s easy to understand why eggshells are porous: a developing chick needs to be able to breathe.
When you get eggs from your chickens or from the grocery store for eating, ideally, you will store the eggs in such a way as to keep them fresh. A fresh egg that has just been laid has either a very small air cell or none at all. But as it first cools and then ages, an air cell will form and increase in size. The size of the air cell gives a good indication as to the age and freshness of the egg. A smaller air cell indicates a younger, fresher egg.
This makes it easy for you to test how fresh an egg is. Take a chicken egg and place it into a bowl of slightly warm water. If the egg is very fresh, it will sink and lie on its side at the bottom of the bowl.
An egg that sinks but doesn’t lie flat on the bottom isn’t as fresh, but it will still be okay to eat. Actually, eggs at this stage are ideal for cooking as hard boiled eggs (but not ideal for use as poached eggs). It’s hard to cleanly peel off the shell on a very fresh egg that’s been hard boiled, but if you let your eggs age a little, then hard boil them, they will be much easier to peel.
If the egg floats in the bowl of water, discard it. It’s unlikely that it will float on top of the water, but even if it just floats up toward the top of the bowl, it’s not very fresh, and you shouldn’t use it.
As a second test and a safeguard against ruining your recipe, if you’re getting ready to make something that calls for eggs and you come across an egg that’s questionable, crack it into a small, separate container, then look at it and smell it. If it smells rotten, discard it. If it smells okay, and if the yolk is holding together and the whites aren’t too runny, it should be fine to use. Egg whites that are cloudy are not at all a cause for concern — on the contrary, they indicate that the egg is very fresh. The egg whites become more clear as the egg ages.