Making ice cream with kids

The Science of Ice Cream

This week in the Virtual Explorers Club membership we have been having fun exploring the science of ice cream. A great way to engage children in exploring states of matter, an important topic that helps us to understand the structure of different materials, whether they are solids, liquids or gases. I always find that edible science experiments engage our children so much more than just telling them about it!

This week we’ve been in our kitchens making butter and ice cream. Aside from a cross contamination incident, which resulted in the reaction “Yuk! It tastes yuk! It’s salty!” most of our explorers enjoyed the fruits of their (or more accurately their parent’s) labour. It’s a tiring business is making ice cream, involving lots of shaking as the cream/milk mixture changes state from liquid to solid.

So how do you do it? Let’s first start with a question, which ice cube will melt faster? One with salt or one without?

Let’s add some real life experience to see if that helps. When it’s icy, or it snows outside, what do we do to make the roads safe? If you live in a cold climate, you may have seen gritting trucks on the road or seen grit on the pavement in the winter. The grit is used to help keep us safe when the weather is cold enough for ice or snow. Grit or gritting salt lowers the temperature at which water freezes, so when we use salt any ice will melt even when the temperature is below the normal freezing point of water. When the freezing point is lowered, we call the process freezing-point depression.

So, which ice cube melted fastest?

You’re right, the one with the salt. Now we can use this knowledge to help us to make some ice cream;

You will need

  • 1/4 cup milk
  • 1/4 cup double cream
  • 1 tablespoon sugar
  • 1/4 teaspoon vanilla
  • 3 cups ice
  • 1/3 cup salt
  • 1 large ziplock bag
  • 1 small ziplock bag

Method

  1. Put the ice and salt into the large bag (leave it)
  2. Mix the milk, cream, vanilla and sugar together in the small bag and seal it shut
  3. Place the smaller bag inside the larger bag and seal it
  4. Now shake both bags, while wearing gloves for 5- 10 minutes- check on the physical state of your ice cream mixture

What’s the science?

To make your homemade ice cream, your ingredients need to get cold enough to freeze .Adding salt to the ice lowers the temperature at which water freezes, you should notice the ice cubes melting as your ice cream ingredients start to freeze.

Shaking the bag transfers the heat from the warm cream into the cold ice-salt mixture which causes your cream to cool quickly and freeze. Your cream begins as a liquid but changes to a solid when it’s been cooled, as it warms up you’ll see it turn back to liquid because it melts. This is a reversible physical change- this means you can go back to where you started.

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