The Science of Egg Freshness: How to Tell If an Egg Is Good

Eggs are a versatile and nutritious staple in many diets, offering a rich source of protein, vitamins, and minerals. But have you ever wondered how to tell if an egg is truly fresh? The freshness of an egg is more than just a culinary concern – it’s a matter of food safety and optimal taste. In this article, we delve into the science of egg freshness and explore effective methods to determine whether an egg is good to use.

Understanding Egg Composition:

To comprehend the science behind egg freshness, it’s essential to understand the composition of an egg. An egg consists of several components, including the shell, egg white (albumen), and yolk. The shell serves as a protective barrier against contaminants and moisture loss, while the egg white and yolk provide essential nutrients for a developing embryo.

The Role of Air Cell Formation:

As an egg ages, changes occur within its structure that can be observed and measured. One of the key indicators of an egg’s freshness is the size of the air cell, which forms naturally as the egg contents contract due to cooling and moisture loss. The older the egg, the larger the air cell becomes.

When an egg is laid, it is warm and has a very small air cell. However, as it cools, the contents contract, leaving a small space at the rounded end of the egg. This air cell serves as a cushion to protect the developing embryo during incubation. Over time, the air cell grows larger as the egg loses moisture through the porous shell.

The Water Test:

A simple and effective method to determine egg freshness is the water test. This involves placing the egg in a bowl of water and observing its behaviour. Fresh eggs will typically lie horizontally at the bottom of the bowl due to the small air cell. As the egg ages, the air cell grows, causing the egg to tilt slightly upwards but remain at the bottom. If the egg stands upright or even floats, it’s a sign that it’s less fresh and should be used promptly.

The Sound Test:

Another way to gauge egg freshness is by gently shaking the egg near your ear. Fresh eggs will have a minimal sloshing sound due to the small air cell. Older eggs will produce a more pronounced and audible sloshing sound as the larger air cell allows the contents to move more freely.

Cracking and Observing:

When cracking open an egg, the visual cues can also indicate its freshness. A fresh egg will have a yolk that sits high, a thick egg white that doesn’t spread much, and a well-defined chalaza (the spiral-like cord that holds the yolk in place). In contrast, older eggs might have a flatter yolk, a runnier egg white, and a less visible chalaza

Storing Eggs Properly

Beyond freshness tests, proper storage plays a crucial role in maintaining egg quality. Eggs should be stored in their original carton in the refrigerator, preferably on a shelf rather than the door, as temperature fluctuations can impact their freshness. The cool temperature helps slow down the growth of bacteria and the breakdown of egg components.


The science of egg freshness is a blend of understanding the changes that occur within an egg as it ages and utilizing simple tests to assess its quality. The air cell size, behaviour in water, sound produced when shaken, and visual characteristics upon cracking are all valuable indicators. By being aware of these signs and adopting proper storage practices, you can ensure that the eggs you use in your culinary endeavours are not only safe but also contribute to the deliciousness of your dishes.


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