Did you know you can make homemade ice cream in a bag in less than 10 minutes with just milk, salt and ice? You don’t even need a freezer!!
This awesome kitchen science experiment for kids involves lots of interesting chemistry and you end up with a great tasting dessert at the end!
What is ice cream?
Ice cream is made up of droplets of fat from milk jumbled up with millions of tiny crystals of ice and pockets of air.
We’re going to use the freezing power of salt and ice to create ice crystals in milk without a freezer!
Homemade Ice Cream In A Bag
What you need to make ice cream in a bag
A large bag of ice
Milk – we used chocolate milk
A tablespoon sugar and a tea spoon vanilla essence – optional
How to make ice cream in a bag
Pour a cup of milk into a ziploc bag. Add the sugar and vanilla essence ( or just use flavoured milk ). Make sure the bag is properly sealed.
Half fill a bigger ziploc 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 longer.
Why does ice cream in a bag work?
Pure water freezes at 0 degrees Celsius. 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.
The ice will feel VERY cold, which is why you’ll need a towel to cover the bag after a few minutes.
Practical applications of salt – why is salt added to roads in cold weather?
During cold weather salt and grit are applied to roads, the salt makes the ice melt even if the air temperature is below freezing point.
Place a mixture of ice and salt in a freezer to investigate whether it freezes or not.
This activity would be perfect for a science club or fun STEM Challenge. You could even have a competition to see who can make the COLDEST ice cream!
See our other kitchen science experiments for kids here.