What you’ll need

  • 125 ml milk
  • 125 ml cream
  • 1.5 tbsp sugar
  • food coloring, e.g., red (optional)
  • flavoring, e.g., vanilla (optional)
  • approx. 0.5 kg ice cubes
  • approx. 120 g salt
  • 1-liter freezer bag with pressure/zip seal
  • 3.5- or 4-liter freezer bag with pressure/zip seal
  • winter gloves
  • measuring jug

How to do it

1. First mix the milk, cream, sugar and maybe a little food coloring and flavoring in a mixing jug.

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2. Next, pour the liquid into the small bag.

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3. Squeeze out the air from the bag and seal it carefully by pressing on the pressure seal. The bag must be watertight so that no salt water can get inside.

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4. Place a few ice cubes and some salt into the large bag and mix them together.

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5. Insert the small bag into the large bag with the ice and carefully seal the large bag.

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6. Put on your gloves and turn the bag over and over for approximately five minutes. As you do so, make sure that the small bag is always surrounded by the ice-salt mixture.

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7. Your ice cream is now ready! The milk mass has frozen into solid ice cream. Retrieve the small bag and rinse off all the salt. Eat the dessert quickly because it will melt much more quickly than normal ice cream from the freezer. But use a small spoon – otherwise the cold will make your teeth hurt. Enjoy!

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Well spotted!

When the bag is shaken, the ice melts and the salt gradually dissolves. This makes the ice water very cold and after a while the milk turns solid.

What’s the secret?

Salt dissolves in water. Because there is also a small thin film of water on the ice cubes, the salt dissolves when it touches the ice.

If this thin film of water is absorbed by the salt and there is still enough salt, the ice on the surface begins to melt again. The dissolving process repeats until there is no salt left.

The dissolving of salt consumes energy in the form of heat. The heat is removed from the environment, i.e., the ice. The saltwater-ice mixture is therefore significantly colder than ice without salt.

When it comes into contact with the cold saltwater-ice mixture, the milk mixture also loses heat, becoming cold and firm.