1 large Ziploc bag (we used a 3 litre one)
1 smaller Ziploc bag (we used a 1 litre one)
2 cups of ice (or a few handfuls)
1/8 cup (or about 2 tablespoons) of coarse sea salt
1/2 cup of full fat milk
sugar to taste (about 1 tablespoon, more if you have a very sweet tooth)
whatever flavouring you like - the chocolate was my favourite and we used a dark cocoa powder (the one you use for baking)
The exact amount of ingredients is not super important for this experiment/ recipe.
This process creates temperatures well below normal freezing so protect your hands with gloves or a towel.
How does it work?
Salt lowers the freezing point of the ice and creates an extra-cold brine (salt water) that absorbs the heat from the milk mixture, causing it to freeze.
Why do you need to shake the bag?
The motion creates smoother ice cream by breaking up large ice crystals and allows the ice cream to freeze uniformly (so no big icy lumps).
How long do you need to shake for?
We paused the video while we were shaking so you wouldn't be jealous of our groovy dance moves but seriously - about the length of a song or two. You can check your ice cream in between and mush it between your fingers to see if you are happy with it.