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STEMingBoredom 27: make ice cream

This is one of the experiments that we like doing the most, can’t think why...

What is interesting about this experiment – apart from giving you ice cream at the end – is that you can observe the change of state in the ice cream as you make it. You can do this observation elsewhere; such as in water, but this is more gradual and happens as you watch it. Water can have three states – liquid, solid (ice) or gas (steam). Here, you’ll gradually observe the change in state from liquid to solid.

How to do it:

This experiment is best done between 2 or 3 people, and not only because you get to treat people to ice cream!

You’ll need:

Half a cup of milk
Half a cup of double cream
Quarter of a cup of sugar
Quarter teaspoon of vanilla extract
Half to three quarters of a cup of table salt
Two cups of ice
Big Ziploc bag
Small Ziploc bag

Put the milk, double cream, sugar and vanilla extract into the small Ziploc bag. Seal the bag to avoid leaks – strictly speaking, it doesn’t have to be a Ziploc bag – but it does stop a lot of mess!

Put the ice into the big Ziploc bag. Take and record the temperature of the ice in the big bag at this point. Add the salt to the ice in the big bag.

Put the small bag inside the big bag and seal it up.

Rock the bag from side to side gently – it doesn’t need to be heavy, just a gentle rocking motion. This is where it’s good to do this with friends – keep gently rocking the bags from side to side for 15 minutes!

Open the big bag and take the temperature again – what do you notice about the difference in temperature to the reading when it was just ice alone?

Get bowls and enjoy your homemade ice cream with the team that made it!

Extension task:

Try adding chocolate chips, or some other commonly used pieces to give a different flavour to your ice cream. In adding these into the ice cream mixture, how does this change the time it takes for the change of state to occur?

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