What do rotten eggs smell of?

eggsperiment step1

Rotten eggs smell really, really bad! But what makes them smell so rotten? My daughter wanted to know because she read a story in which something was described as smelling of rotten eggs. So, she did an experiment to find out the answer:

Rotten eggs have a particularly smelly smell and one that it quite unmistakably the smell of rotten eggs! To understand how this smell is made, we need to know a bit about what eggs are made of. Inside the egg’s shell, the white (albumen) and yellow (yolk) parts are made of chemicals called ‘proteins’.

Almost as soon as an egg has been laid, changes start to happen to these proteins (so, it’s a good idea to eat an egg when it is nice and fresh). As an egg gets older, bacteria inside it start to change the proteins in the albumen and yolk, producing a gas called hydrogen sulfide. Hydrogen sulfide (which has the chemical formula H2S) is a stinky, poisonous gas, which is also found in volcanoes and sewers. So, it’s best to avoid hydrogen sulfide for safety as well as smelly reasons!

Rotten ‘eggsperiment’

The aim of my daughter’s experiment was quite simple: take a fresh egg, make it go rotten, then smell it. It’s a simple experiment that you can do at home (see these instructions) but please take note of these hints:

  1. Ask a grown-up to help you – especially with finding a safe place to leave your egg and with opening the container.
  2. Rotten eggs contain bacteria, so don’t get any egg near your mouth or eyes and make sure you wash your hands thoroughly!
  3. The smell is really bad and the gas isn’t good for you, so don’t breathe it in too deeply and don’t get any egg on your clothes or skin or else you will stink!

So, my daughter took a plastic container with a well-fitting lid and put a fresh hen’s egg inside. She cracked the shell of the egg using a fork and added some bacteria (by spitting onto the egg), then sealed the container with the lid. Then, she left the container in a warm, sunny spot in the garden for a week. Here’s a step-by-step photo guide to her experimental set-up:

I recorded the moment that they opened the contained to take a sniff, take a look at our results video!

As you can see, her conclusion is that rotten eggs smell DISGUSTING! Why not try the experiment for yourself and see what you think?!

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