Making Ice cream

What could be better than making ice-cream on the last day of the year?! (A Science Experiment of course!)

Here are the instructions - Try this at home over the holidays!

What you need:

300ml cream

2 tbsp castor sugar

1 tsp vanilla essence

2 trays of ice cubes

6 tbsp rock salt

1 medium sized zip-lock zip-lock bag

1 large sized zip-lock bag

Step 1: Place the cream, sugar and vanilla into the medium sized zip-lock bag and combine the ingredients.  Be sure to zip up the bag securely first.

Step 2: Place the ice into the larger zip-lock bag.   

Step 3: Spoon the salt over the top of the ice in the larger zip-lock bag.

Step 4: Place the medium bag containing the cream mixture inside the larger bag on top of the ice and salt and zip up the bag securely.

Step 5: Shake and massage the bag for five to ten minutes or until the mixture becomes the consistency of ice cream. 

Step 6: You might like to wrap the bag in a tea towel or wear oven mitts while you’re shaking as it can get quite cold!  It’s also a good idea to do this part outside as the water can drip out of the bag as the ice begins to melt.

Step 7: Once ready, remove the bag of ice cream and give it a wipe to remove the salt from the outside of the bag.

Step 8: You now have your own home-made ice cream!

What's the Science behind this?

Salt mixed with ice causes the ice to melt. When salt comes into contact with ice, the freezing point of the ice (0°C) is lowered (-21.1°C)  By lowering the temperature at which ice is frozen, we are able to create an environment in which the milk mixture can freeze. The fat particles in the milk smash into each other and make big molecules of ice cream!

By the way…

When sea ice forms, most of the salt is pushed into the ocean water below the ice. Water below sea ice is really salty and is more dense than surrounding ocean water, and so it sinks. In this way, sea ice contributes to the ocean's global "conveyor-belt" circulation.

The Antarctic Circumpolar current has a lot of dense salty water and has a lot to do with ocean currents and weather patterns.