Testing eggs for freshness
Testing eggs for freshness is a fun science experiment you may try in school or at home.
It can sometimes be hard to tell if your eggs have gone bad just by looking at them. There’s an easy way to tell if an egg is fresh or not and you don’t have to break it open either!
You need: eggs, glass or bowl with water.
What to do: fill a glass (or bowl) with cold water and place the egg inside. Make sure there’s enough water to completely cover the egg.
Fresh eggs typically rest at the bottom of the glass. If the egg floats, it’s old and may be rotten.
For a very accurate scientific test, you’ll need to crack open the egg to observe its appearance and smell it to be certain eggs are good or bad.
Sink or float? So, why the bad eggs float? When an egg starts to rot, the decomposition occurs. Egg shells may seem pretty solid, but they are in fact slightly porous. The water inside the shell slowly evaporates through the shell pores and is replaced by the gas hydrogen sulfide (H2S) that is produced as the egg rots.
Many food products (vegetable, fruit, etc.) give off gases when they go off, and they often smell!
As the egg gets older it ends up with more gas inside and less water; this makes egg lighter and in fact less denser than water, so the stale eggs float.
A fresh egg sinks in pure water because the egg yolk, egg white, and gases have enough mass that the density of the egg is greater than the density of water.