Do Rotten Eggs Float Or Sink

You might have heard that rotten eggs float, whereas fresh eggs sink. But is that really true? In this article, we'll explore the scientific reasons behind why eggs float or sink and discover the factors that can affect their buoyancy.

How Buoyancy Works

Buoyancy is an upward force exerted by a fluid that opposes the weight of an immersed object. If the upward buoyant force is equal to or greater than the downward gravitational force acting on the object, the object will float. Conversely, if the buoyant force is less than the gravitational force, the object will sink.

Egg Structure

To understand why eggs float or sink, we need to consider their internal structure. An eggshell is made of calcium carbonate, which is relatively heavy. Inside the shell, the egg is composed of albumin (egg white) and yolk. The yolk is denser than the albumen and contains a higher proportion of fat.

Fresh Eggs vs. Rotten Eggs

When an egg is fresh, the air cell inside the egg is small, and the albumin and yolk are tightly bound together. This structure results in a relatively uniform density throughout the egg, causing it to sink in water.

As an egg ages, the air cell expands, and the albumin becomes thinner and less dense. Additionally, bacteria and other microorganisms begin to decompose the egg, releasing gases that further reduce the density of the egg. This change in density causes the egg to become more buoyant, eventually leading it to float.

Factors Affecting Buoyancy

Several factors can affect the buoyancy of an egg, including:

Age: As mentioned earlier, older eggs are more likely to float due to the decomposition process.
Water Temperature: Warmer water has a lower density than cold water. Therefore, eggs are more likely to float in warm water.
Salt Concentration: Saltier water has a higher density than freshwater. Eggs are more likely to float in freshwater than in saltwater.

Exceptions to the Rule

While the general rule is that rotten eggs float and fresh eggs sink, there can be some exceptions. For example:

Very old eggs: Extremely old eggs may have lost so much moisture that they become less dense and float, even if they are still fresh.
Eggs with damaged shells: Eggs with cracks or holes in the shell may allow water to enter, affecting their buoyancy.

Practical Applications

The ability to determine whether an egg is fresh or rotten by its buoyancy has practical applications in food safety. The "float test" is a simple and effective way to check the freshness of eggs before cooking or consuming them. It is recommended to discard any eggs that float in cold water.