There’s a lot of things that the “sell by” date on an egg carton can’t tell you. It can’t account for the temperature of your fridge — eggs kept in the back, where it’s coldest, last longer than those stored on the door, which is further from the cooling mechanism. It doesn’t know how long the eggs sat out in the delivery truck before it got to the supermarket, or how long they sat in your car while you were running your weekly errands. And what about the eggs you find buried in your fridge that are a bit past the sell-by date: are they still good to use? There’s a very, very simple trick that will tell you if your eggs are still good that literally takes seconds: the float test.
What's the Float Test?
Inside their shells, eggs have a tiny air bubble that provides a little cushion so the whites and yolks aren’t damaged if they get jostled around. When eggs are fresh, this bubble is very small — if you hard boil a super-fresh egg, you’ll be able to see how big it is, as it leaves a visible impression on the egg.
Eggshells are “semi-permeable membranes”, which means that air can both enter and escape the egg, albeit very, very slowly. With farm fresh eggs, there is a thin coating on top of the eggshell called the bloom (or cuticle), which provides an extra layer of protection, sealing the microscopic holes in the eggshell to keep bacteria out of the egg. When factory-farmed eggs are processed, this layer is washed off, which is why eggs must stay refrigerated to slow the airflow between the inside of the egg and the outside environment.
How Does the Egg Float Test Work?
Now, to the float test: as eggs age, the air pocket inside steadily grows larger and larger, meaning that when it gets old enough, it will float. A fresh egg with a small air pocket will immediately sink in a glass of water.
But let’s say you forgot to do the float test and already cracked your eggs: what can be done? Old eggs will smell of sulfur, so if you eggs have any sort of odor, toss them. If they look and smell good, you’re good to go.