The Science Behind Floating and Sinking Eggs: What It Means for Freshness

Have you ever wondered why some eggs float while others sink when placed in water? The answer lies in the science behind egg freshness. In this article, we will explore the reasons behind this phenomenon and what it means for the freshness of your eggs.

The Eggshell’s Porosity

When an egg is first laid, its shell is covered with a natural protective coating called the bloom or cuticle. This thin layer acts as a barrier, preventing air and contaminants from entering the egg. Over time, however, this protective coating may wear off or be washed away during cleaning.

As an egg ages, its shell becomes increasingly porous. This means that air can gradually penetrate through the shell and into the egg’s interior. The more air inside the egg, the more buoyant it becomes.

The Air Cell Formation

As an egg ages, another important change occurs within its structure – the formation of an air cell. This air cell develops at the wide end of the egg as moisture evaporates through pores in the shell.

The size of this air cell increases over time due to both moisture loss and carbon dioxide release. As a result, older eggs will have larger air cells compared to fresher ones. When you place an older egg in water, this larger air cell creates buoyancy and causes it to float.

Freshness Test: Sink or Float?

Now that we understand why some eggs float while others sink, let’s discuss how you can use this knowledge to determine their freshness.

To perform a simple freshness test at home, fill a bowl with water and carefully place your eggs in it one by one. If an egg sinks to the bottom and lies flat on its side, it is considered very fresh. These eggs are ideal for poaching or frying as they hold their shape well.

On the other hand, if an egg stands upright on the bottom of the bowl or floats to the top, it is no longer fresh. The more it stands upright or floats, the older the egg is likely to be. These eggs are still safe to eat but are better suited for hard-boiling or baking, where appearance is less important.

Storing Eggs for Maximum Freshness

To ensure your eggs stay fresh for as long as possible, proper storage is key. Ideally, store your eggs in their original carton in the refrigerator rather than in the door where temperatures fluctuate.

Remember that eggs should always be stored with their pointed end down. This helps keep the air cell at the wide end intact and minimizes moisture loss through evaporation.

Additionally, it’s best to use older eggs first before using fresher ones. By following this simple rule, you can make sure your eggs are used within a reasonable time frame and enjoy them at their best quality.


Understanding why some eggs float while others sink provides valuable insights into their freshness. By performing a simple sink or float test at home and storing your eggs properly, you can ensure that you’re using them at their peak quality. So next time you’re unsure about an egg’s freshness, try this easy test and enjoy delicious meals with confidence.

This text was generated using a large language model, and select text has been reviewed and moderated for purposes such as readability.