Holiday fun: the science of ice cream

Here’s a way to keep the kids occupied during school holidays – and learn a bit of science while they’re at it.

Did you know that making ice cream can be as easy as shaking and rubbing a bag of ingredients together?

The hardest part will be trying to decide what flavour to make it, and if you want to be safe and go for something like a hazelnut flavour or really go wild and try Marmite-flavoured ice cream. Let us know what flavours you tried – we love hearing feedback from the experiments.

WHAT YOU WILL NEED:

■ measuring jug/ cups

■ 1 medium clear ziplock bag and 1 large clear ziplock bag

■ 2 trays of ice cubes

■ 6 tablespoons of table salt

■ 200ml of cream

■ 100ml of full-fat milk

■ 2 tablespoons of caster sugar

■ flavour of your choice

■ tea towel/warm gloves

WHAT YOU NEED TO DO:

With your measuring jug or cups, measure out 200ml of cream and 100ml of milk.

Pour the cream and the milk into the medium ziplock bag.

Add 2 tablespoons of caster sugar to the cream and milk.

This is where you get brave and adventurous and add your choice of flavouring to the medium bag.

Remove all the air and seal the bag. Double-check to make sure it is closed properly and there are no holes in the bag, as we don’t want the mixture to leak.

Grab the large ziplock bag and place six tablespoons of table salt inside it.

Add your ice cubes to the large ziplock bag. Make sure you have at least 4 handfuls of ice in your large bag.

Put the medium-sized ziplock bag with your ice cream mix inside the large ziplock bag.

Remember to double-check that BOTH bags are sealed tightly.

Wrap your large ziplock bag in a tea towel or put a pair of gloves on. This will help you to keep warm as your job now is to shake, shake, shake that bag and give it a good rub with the ice around the medium bag. You will need to shake continuously for at least 5 minutes.

Check to see if the mixture has turned into ice cream, if not keep shaking and rubbing your bag until you feel like you now have yummy ice cream.

Eat and enjoy and add your favourite toppings like Strawberry, Chocolate, or Caramel sauce.

THE SCIENCE BEHIND IT:

EMBRACING SCIENCE

House of Science is a charitable trust which gives primary school aged children access to comprehensive, bilingual resources to improve scientific literacy in the classroom. It was founded in 2013, by CEO –a biochemist and secondary school science teacher for 15 years – after she developed a growing sense of concern about the lack of science knowledge students had when they arrived at high school. Nearly 10 years on, House of Science has grown to 19 branches around New Zealand, with more popping up when funding allows.

Water normally freezes at 0 degrees Celsius, but adding salt to the ice causes the freezing point of the ice to be lowered. A 10% solution of salt in water lowers the freezing point of water to -6 degrees Celsius and a 20% solution will lower the freezing point to -16 degrees Celsius.

Saltwater, therefore, needs a lower temperature to become a solid. This means that you will have ‘‘supercooled water’’ touching the medium bag, which

Chris Duggan

helps to freeze the ice cream solution inside.

This activity is a great lead-in to the House of Science Kit ‘‘Moo to You’’ where students are introduced to how living things are classified, to grow their own pastures, to make silage, and participate in a lovely, messy hands-on activity that both explores and compares the stomachs and digestive processes of humans and cows.

The composition of different types of mammalian milk are evaluated and an on-line supermarket scavenger hunt illustrates the number and variety of milk products available for sale in supermarkets.