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24/09/2017

Ice Cream in a Bag

Use a little bit of science to make a tasty ice cream treat without a freezer or ice-cream machine.

What You Need:

  • 1/4 cup of Cream

  • 1/4 cup of Milk

  • 1/2 teaspoon Vanilla

  • 1/4 cup of Rock Salt

  • 2 cups of Ice

  • Tea towel or Oven Mitts

  • Snack-Sized and Sandwich-Sized Zip-Lock Bags

  • Ice Cream Topping or Add-In of your choice (we used Milo, because yum!)

What You Do:

  1. Add the Cream, Milk, Vanilla and Ice Cream Topping to a Snack-Sized Zip-Lock Bag. Be sure to squeeze as much air out of the bag as you can before sealing it. You might want to place this bag into a second bag to avoid any leaks, making sure to again remove as much air as possible before sealing it.

  2. Put the Rock Salt and Ice into a Sandwich-Sized Zip-Lock Bag, place the snack-sized bags with your ice cream mix inside and seal it.

  3. Get your groove on and shake, shake, shake the bag for approximately 10 min. The bag will get very cold so its a good idea to wrap it in a Tea Towel or wear Oven Mitts while shaking.

  4. Enjoy your ice cream treat straight from the bag. Yum!

How It Works:

When salt and ice mix, the freezing point of the ice is lowered. The more salt is added, the lower the temperature can get before the saltwater solution freezes (e.g. water normally freezes at 0℃, a 10% salt solution freezes at -7℃ and a 20% solution freezes at -17℃). In our experiment, when salt is added to ice, some of the ice melts because the freezing point is lowered. However, the heat that melts the ice has to come from somewhere, in this experiment, it comes from the relatively warmer cream mixture. The shaking moves the warmer cream mixture from the inside to the outside of the bag so it can freeze evenly. It also adds air so it’s fluffed up a little bit. Tasty, tasty science!

What Next?

Try experimenting with different ratios of cream and milk to see if it affects the texture of the ice cream. You can also test what happens if you repeat the experiment without adding salt or adding more salt. On a more delicious note you can try adding in different toppings to make your own flavoured ice-cream. Or maybe you want to try and make your own Magic Chocolate Topping to go with your ice cream treat. Yum!