Crystals. Pores. Density. And how to pick up the right egg with one simple trick.
1-Minute NomNom
Why do we put an egg into a bowl of water to see if it is fresh? And how can you tell if the hard-boiled egg you have just been served in a cafe is fresh?
The eggshell is formed mostly of calcium carbonate (CaCO3) crystals. According to Scientific American, there can be 7000 or more microscopic pores in the eggshell. You can see these pores if you look at an egg under a magnifying glass.
Air pocket is visible at the bottom of the egg
These pores allow air and moisture to pass through (that’s how unhatched chicks breathe!). As a result, an air bubble forms inside the egg. Freshly laid eggs have a smaller air bubble. As an egg ages (egg-es?), however, the liquid inside evaporates through the shell, allowing more air to enter. A bigger air bubble is formed.
You can use this property to find out how fresh an egg is. Once the egg is peeled, the size of the crater at the base of the egg tells you how fresh the egg is. The smaller the crater, the smaller the air bubble was, and the fresher the egg. Sometimes, if the egg is super fresh, you might not even see a crater!
You can now use this knowledge to see whether the hard-boiled egg you are being served in a restaurant is fresh! But what if you want to know before the egg is peeled? The trick is to put it in a container of water and see if it sinks or swims.
A fresh egg will sink in a container of water because it is denser (its air bubble is small). A rotten egg on the other hand will float as it is less dense (because its air bubble is much bigger). Simply watch this BBC video to see how you we can do this!
With this simple trick grounded in science, you will be able to know how fresh your eggs are, especially for recipes that call for only the freshest eggs.
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photos: in order – istockphoto/blackred; depositphotos/Klanneke; akulamatiau
