Rotten Eggs Float
May 6, 2010 at 12:15 am Chad Upton 1 comment
Whether you throw away the carton and use the egg holder in your fridge or you just don’t believe the expiry date, there will come a time when you question the edibility of eggs.
There is an easy way to test them.
Fill a container with water and gently place the egg inside it. If it sinks, it’s good to eat. If it floats, throw it out. If it weighs the same as a duck, it’s a witch.
Why?
Eggs naturally have a small air pocket in them. In fact, a bright light is used during a process called candling to determine the size of this air cell. The size of the air cell is used to determine the grade of an egg. Grade AA eggs have the smallest air cell, and as the air cell gets large the egg is given a lower grade (A, B…etc).
This air cell increases as the egg ages. There are two schools of thought about why. Some say the eggshell is porous and allows some liquid to escape and air to enter. Others say a chemical reaction takes place inside, which results in the larger air chamber and the awful smell when they are rotten. I couldn’t find a definitive answer to why the air cell increases in size, but nobody disputed the fact that it does.
Because the air cell increases, it makes the egg less dense, meaning it will float in water with enough time.
The smell of rotten eggs is a popular description for the smell of sulfur. There’s good reason for that, eggs contain a fair amount of sulfur because it is necessary for feather formation. This smell becomes more prevalent as eggs age.
Thanks to my wife Kristen for this secret.
Broken Secrets | By: Chad Upton
Source: Eggs WP, Sulfur WP, What’s Cooking America, O Chef
Entry filed under: Around The House, Be Frugal, Demystified, Food and Drink. Tags: bad, egg, float, sink, smell, sulfur, water.
Broken Secrets 
1.
Matt | June 4, 2010 at 1:48 pm
I’d be inclined to believe evaporation. It seems to be similar to the loss of liquid in an aging barrel of beer (check out http://en.wikipedia.org/wiki/Aging_barrel#Angels.27_share ) . Basically – the inside of fridges is a pretty dry environment due to the de-humidifying done by the cooling process (think of air conditioners – they de-humidify as a byproduct of cooling. Fridges are similar.). So you’d lose liquid in the egg just as you would in a barrel of liquor.
A chemical reaction in the egg would only change the overall density of the egg if it increased the size of the shell. If the shell is non porous, it’s impossible to get an overall less dense egg by a chemical reaction inside if the chemical reaction doesn’t increase in volume (conservation of mass).