Eggs: Freshness + Bonus trick.

Updated: Jun 1, 2020

This article is all about the science-y part of eggs. What do they contain and how do you tell it's freshness when it is still in the shell?! Read on to find out how to do it and why that works.


All sorts

Edible eggs include ostrich eggs, goose eggs, duck eggs and quail eggs. But today I am going to talk about the most common one, the chicken egg.


The chicken egg consists of three main parts: the shell, the egg white and the egg yolk. The egg shell is not consumed by humans, so let's not get into that.


The egg white contains mostly water and protein and it is almost translucent when raw. When you cook the egg the proteins denature. As a result, the egg white solidifies and turns opaque. This process starts when the egg white reaches a temperature of 60°C. You can read more about denaturing here: Proteins.


The egg yolk contains fat, protein and water. This also denatures and solidifies when you heat it, but at a higher temperature: 68°C. This is one of the reasons why soft boiled eggs have a runny yolk, but a solid egg white. The inside of the yolk simply does not reach the temperature it needs to denature.


Glass of water

A glass of water is basically all you need. Carefully pop the egg in and look at it's floating behaviour. Check the infographic below to "read" your egg.


1. Take a wide glass and fill it halfway with water. Carefully lower the egg in.

2. If the egg sinks and lies down on its side on the bottom of the glass it is quite fresh (1-2 weeks old)

3. If the egg sinks, but sits upright it isn't superfresh anymore (2-3 weeks old). You can still use it for baking or making an easy to peel boiled egg.



The Science

The shell of an egg is porous. This means that it contains pores/ tiny holes through which some substances can move. In this case that is moisture and air. Slowly the egg white starts drying and moisture moves out of the egg through the pores. Simultaneously air is pulled into the egg to make up for lost space.


The air bubble slowly grows, thus giving us the opportunity to use this handy trick.


Bonus trick

Found a loose egg in the fridge, but can't remember whether it is boiled or not? Lay the egg on its side and give it a little spin. Very briefly put your fingers on top to interrupt its spinning. If it completely stops your egg is cooked. If it continues spinning it is raw. Physics!


I will explain. When you spin the egg, you spin the insides too, logic. When you briefly stop it, you don't stop the liquid inside, so when you let go, the still spinning insides make the outside spin again.


Now you've checked some things about your egg it is time to make something delicious, head to some basic recipes here. Want to learn how to crack it first? Click here.

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