The simplest way to check the freshness of an egg is to gently place it in a glass of water. Fresh eggs sink, while old ones float. This is known to many, but why does this happen?
An egg consists of albumen (white), yolk, and a small air pocket. All three components affect the overall mass of the egg. In a fresh egg, the air pocket is less than 3.175 mm thick. Many believe that the presence of the air pocket causes the egg to float, but if that were the case, fresh eggs would also float.
Fresh eggs sink to the bottom due to their density, which is greater than that of water. Density is defined as mass divided by volume, so the greater the mass of the egg, the higher its density. In an old egg, the yolk and white begin to decompose, and part of the mass turns into gas. Thus, the air pocket in old eggs increases because it contains more gas. However, this is not the only reason why an old egg floats.
Why Does an Old Egg Float?
The secret lies in the shell. The eggshell is porous, which facilitates gas exchange during the development of the embryo. Some gases escape from the air pocket, and while air also enters, the amount of gas escaping exceeds the amount entering, which reduces the overall mass of the egg.
Now, let's recall the density formula. The volume of the egg remains more or less constant due to the shell. However, as gas escapes, the overall mass of the egg becomes less than that of water. As a result, the density of the egg turns out to be lower than the density of water, which explains why an old egg floats.
Thus, a larger air pocket gives the egg buoyancy, but since gas also has mass, the overall mass of the egg remains the same, even if the yolk and white decompose. This is due to the porosity of the shell, which allows gas to escape.
Can You Eat an Egg if It Floats?
If you store eggs in the refrigerator and notice that they start to float in cold water, don’t rush to throw them away. For example, quail eggs can “float” as early as the tenth day after being laid due to rapid moisture and weight loss. However, if chicken eggs float, it may indicate that they have been stored too long, and it is better not to consume them.
If you decide to boil eggs that have floated in water, there’s no need to worry. During cooking, eggs lose moisture, and they can be considered safe to eat. But if you notice other signs of spoilage (such as cracks in the shell or an unpleasant smell), it’s better to avoid cooking them.
To keep eggs fresh for as long as possible, store them in the refrigerator at a temperature between 0 and 4 degrees Celsius. Also, avoid placing eggs near strongly scented foods (such as onions or garlic) so they do not absorb unpleasant odors.
If an egg sinks immediately to the bottom and lies horizontally, it means it is fresh. However, over time, chemical processes inside the egg change the consistency of the white and yolk, making them more liquid. If an egg floats in water with the blunt end up, it is about a week old and still edible. If it stands vertically, it is about 2–3 weeks old. An egg older than a month will float completely, and it should not be eaten.
Some add a little salt when boiling eggs to prevent the contents from leaking out of cracked eggs. However, it should be noted that in this case, determining the freshness of the product can be difficult. Salt increases the density of water, and if an egg floats in salted water, it does not necessarily mean it is not fresh. However, if it lies horizontally even in salted water, it guarantees its edibility.
It is important to remember that consuming spoiled eggs can lead to health problems, so it is not worth the risk. If you are in doubt about the freshness of the eggs, it is better to check them for spoilage before cooking.
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