How to make ice cream with salt and ice

Did you know you can make a homemade ice cream in just a few minutes? All you need is milk, ice and salt to create the perfect ice cream and science experiment for the kids.

WHAT YOU NEED TO MAKE ICE CREAM IN A BAG

A large bag of ice

Salt

Milk  - preferably flavoured milk

A tablespoon sugar and a teaspoon vanilla essence – optional

Ziploc/ sealed bags

Tea towel

HOW TO MAKE ICE CREAM IN A BAG

• Pour a cup of milk into a sealable plastic bag. Add the sugar and vanilla essence ( or just use flavoured milk ). Make sure the bag is properly sealed.

• Half fill a bigger sealable bag with ice and add a good amount of salt.

• Put the milk bag into the ice bag and give it a good shake.

• Keep the milk in contact with the ice as much as possible.

• Keep rolling the ice over the milk, the ice in the bag will get VERY cold, so  put a towel around the bag to protect your hands.

• Check the milk after 5 minutes, it should be a similar consistency to ice cream, if not keep going for a bit

WHY DOES ICE CREAM IN A BAG WORK?

Pure water freezes at 0°C. The addition of salt lowers the freezing point by a few degrees ( freezing point depression ). This means when salt is added to the ice in the outer bag, the ice (which is at 0°C) is above its freezing point, so starts to melt. Melting needs energy which in this case comes from the milk mixture in the inner bag. Heat energy is absorbed from the milk making ice crystals form between the tiny fat molecules.

The more salt that is added to the ice, the lower the freezing point. For the ice to melt heat must be absorbed from the surroundings ( in this case the milk mixture ) causing it to freeze.


Adapted from: https://www.science-sparks.com/how-to-make-ice-cream-with-ice-and-salt/