Imaginative Teaching Resources & Inspirational Career Ideas from the Chilled Food Industry
Easter is one of our favourite times of year and so we’ve put together some eggs-citing food science egg-speriments to try at home, or in the classroom. And guess what they’re all based on…..?
Prepared with all the right ingredients and egg-quipment our young scientists Morgan and Tilly got cracking…that’s the last of the puns! Starting with floating eggs.
Eggs – can float and sink!
You’ll need: six eggs, large jug of water, a waterproof pen, a calendar
We put one egg to one side (out of the fridge but make sure it’s safe and not likely to get broken) for 4 weeks old (be careful not break!) We marked four weeks
on the calendar.
After four weeks we labelled it ‘old’ and took a fresh egg (new) and put them in a large jug of water.
The old egg floats to the top and the fresh eggs sink. This is a great way to test your eggs without cracking them.
Fresh eggs sink because their contents are mainly protein and fat-containing yolk and proteinaceous white so that the density of the egg is more than the water so it sinks.
(Density is the mass per unit of volume – physics in action)
When an egg ages it starts to go ‘off’ – it begins to decompose. This process means that the substances inside the egg begin to break down and more of the contents are converted to gases. A gas bubble forms inside the egg. As we have seen in some of our previous experiments the eggshell is porous so some of the gases escape through it but enough stay inside the shell to make a pocket of gas. Gas is less dense than the yolk and white so this means that the density of the egg decreases as it ages as the gas inside gets bigger. Once the air pocket is big enough it makes the egg less dense than the water it is in and then the egg floats.
It’s a common misconception that rotten eggs float because they contain more gas. If the inside of an egg rotted and the gas couldn’t escape, the mass of the egg would be unchanged. Its density would also be unchanged because the volume of an egg is constant (i.e., eggs don’t expand like balloons). Changing matter from the liquid state to the gas state doesn’t change the amount of mass! The gas has to leave the egg for it to float.
For more experiments with eggs and science have a look at:
How to make a fresh egg float!
We took our fresh egg and put it in another glass jug. It sank. To make the egg float we need to increase the density of the water so that the egg is less dense than the water. To make water dense you can add salt. We added the 4 tablespoons of salt to the jug and stirred well.
The water was very salty! Now when we added the egg to the water was less dense than the water so it floated!
The Egg Info people have lots more information on this: www.egginfo.co.uk
Making Chalk from Eggshells
Once you’ve enjoyed eating your eggs don’t throw the shells away – you can make them into chalk. You’ll need: eggshells, hot water, plain flour, food colouring, an ice cube tray and a pestle & mortar or food processor. Here’s how:
Take five eggshells, wash them and dry them in the oven on a low temperature for 5 minutes. You’ll need an adult to help with this.
Once dry put the eggshells in a mortar and pestle (or a food processor) and grind until you have a very fine powder – so it doesn’t feel gritty. This can take a little while in the mortar and pestle!
Then place the eggshell powder in a bowl and add a teaspoon of plain flour. Add enough hot water to make a stiff paste. Add some food colouring to make your coloured chalk – we chose purple.
Keep stirring to make sure it all turns to your chosen colour.
Place the mix into ice cube tray to dry. This can take a few days to dry fully – but you can form into a chalk shape using kitchen paper. We placed over a radiator to dry.
Don’t use on a chalk board as it can scratch but it’s great for using outside!
Egg to chalk – how did that happen?
Egg shells contain calcium carbonate and this is the same as in normal chalk you would use for drawing. Calcium promotes bone and muscle health – each eggshell contains around 2 grammes of calcium.
Make an all-yellow egg – how to scramble an egg before you boil it
For this experiment you’ll need a raw egg (in its shell) and pair of tights and some elastic bands.
How we did it
We placed the egg in one of the legs of an old pair of Tilly’s school tights. We secured it in the middle with elastic bands either side of the egg in the middle of the leg so that the egg can’t roll around in the leg of the tights.
Holding the tights with a hand at each end of the leg with the egg in the middle we moved both hands in circular movements to spin the egg and then pulled apart suddenly to let the spin create centrifugal force on the egg. You have to do this for a quite a while!
We then boiled the egg for about 10-15 minutes and when cooled peeled the egg. Get an adult to help boil the egg. Take care – when peeling the shell is very hard to come off the egg. You’ll see you’ve turned it golden!
This video also explains the process (links to external site) – How To Make A Golden Egg | Housing a Forest
To check that your egg is yellow inside you can check with a torch (we used our UV torch light!)
An egg that has been fully scrambled inside will let very little light through , whereas an egg that hasn’t been spun will be much brighter as it can let the light pass.
By spinning the egg in the tights we have created centrifugal force , which forces the centre of the object – which in the egg is the yolk towards the outside. This mixes the yolk and white together so when the egg is boiled the egg inside has turned completely yellow!
If you’re not too eggs-hausted (!) you can try more of our Easter-themed Store Cupboard Science ideas on this site:
Which chocolate egg give the longest lasting enjoyment when you eat it? Milk chocolate vs dark chococlate? It’s all in the science:
Milk chocolate has more fast-melting fat molecules than dark chocolate, The dark chocolate contains more cocoa powder which makes it melt more slowly in your mouth. Find out more in our experiment.
And finally – the science of meringues, egg white getting fluffly!