I know this little experiment is designed for kids, but it’s a load of fun making them as adults! We made some on little sticks and served them as cocktail stirrers – works a treat!
Scientific Principle: Saturation
Time required: 3-7 days
Watch in awe as you grow your own edible, crunchy, candy crystals – the longer you leave them, the bigger they grow!
- Wooden skewer
- Clothes peg
- Tall, narrow, clean glass or jar
- 1 cup of water
- 2-3 cups of sugar
- Food colouring
Heat the water in a saucepan over a low heat until it is simmering.
Slowly add the sugar, stirring constantly, making sure that the sugar dissolves in the water before adding more.
Keep adding the sugar until the water starts to look cloudy. This is the point where no more sugar will dissolve.
Remove the pan from the heat and allow to cool.
Wet the skewers with water, then roll them in the remaining sugar – leave for a few minutes to dry.
Once the sugar solution has cooled, pour it into the glass or jar and add food colouring.
Clip the clothes peg onto the wooden skewer so that the skewer is suspended in the centre of the glass and is approximately 2 cm (1 inch) from the bottom of the glass.
Leave the glass on a table where it will not be knocked and watch it grow.
The first crystals should form after 3 days and will continue to grow bigger.
You can help your candy crystals to grow by checking for, and removing, any crusty film that forms on the surface of the solution.
When you are happy with the size of your candy crystal, remove it from the solution and leave it out to dry for a couple of hours before eating.
The Science Behind the Rock Candy
If you pour a spoonful of sugar into a glass of cold water and stir it, the sugar will dissolve into the water. Eventually, if you keep adding sugar to the water it will stop dissolving. However, if the water is heated, more sugar can be forced to dissolve in the water, creating what is called a supersaturated solution . As the water cools back down, the supersaturated solution becomes unstable since it contains more sugar than it can hold. The sugar then starts to come out of the solution and reforms as solid sugar crystals.
When the sugar starts to come out of the solution it finds the lowest energy surface to form on. As it takes less energy for the sugar crystals to form on top of other crystals than to try and form on their own in the solution the sugar rolles skewers act as seeds for the new sugar crystals to grow. The more the sugar solution cools, the more sugar crystals come out of the solution – and the bigger the candy crystal grows.
- Can you think of ways to flavour your candy crystals with peppermint oil or vanilla essence?
- Do you think this will change the structure of your candy crystals?
- Can you make crystals with other crystal-forming materials like salt? Do the crystals look the same or different?
- How big can your crystal candy grow? Will it keep growing forever or eventually reach a maximum size? Why do you think that is?
Reproduced from The Science Cookbook by Dr Michelle Dickinson, published by Nanogirls Labs Limited, RRP$49.99, available nationwide
Text © Nanogirls Labs Limited | Photography © Magic Rabbit Limited