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  • Writer's picturemeredith conaty

Ice cream in a bag

This one is half science experiment, half cooking... a whole exciting activity for a lockdown afternoon tea!

This activity uses the principal that you can transfer heat from one place to another, as two substances next to each other will try to reach an equal temperature. If one is much colder than the other, it will take heat from the warmer one. In this case, we will use very cold ice and salt to remove heat from a milk and cream mixture. This will freeze the milk and cream mixture, creating ice cream!

By mixing salt and ice together, you can lower the freezing point of the water, and cool it down rapidly to below zero. Did you know that salt water (which is about a 10% solution of salt and water) freezes at -7oC! And the more salt you add, the lower the freezing point - a 20% solution wont reach its freezing point until -17oC. In this experiment we are making a very cold solution of ice and salt around the ice-cream mixture, and transferring the heat out of the milk into the very very cold salt-ice mix. The salt and ice is heating up, and the milk mixture cooling. We will shake it as it cools to aerate it, and create a tasty ice cream snack!

To make your own ice-cream in a bag you will need:

  • 1/4 cup of cream

  • 1/4 cup of milk

  • 1/2 teaspoon of vanilla

  • 1/2 teaspoon sugar

  • 1/4 cup salt

  • 2 cups ice

  • 2 snap lock bags

Step 1: Mix cream, milk, vanilla and sugar in one of your snap lock bags (the smaller of the two if you have different sizes). Squeeze as much of the air out of it as you can, so that it is sealed in tight.

Step 2: Put the salt, ice and the sealed plastic bag with the milk mixture, into the second snap lock bag and seal it tightly.

Step 3: Shake shake shake! You will need to shake the bag for about 10 minutes. It will get VERY cold so you might need to wrap it in a tea towel to hold it while you shake it.

Step 4: Enjoy your ice cream with your favourite toppings!

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