Ice cream making was a fun way to combine science and a tasty treat at some of this year’s STEM events. You can see and learn about chemistry and celebrate what you’ve learned at the end by eating ice cream!

There are several science experiment recipes for making ice cream, but this one worked well for us. The ingredients are pretty simple:
  • 1 cup half & half
  • 1/3 cup salt
  • 2 tablespoons sugar
  • 1 teaspoon vanilla
  • 1-2 quarts of ice (approximately)
  • 1 resealable gallon-sized bag
  • 1 resealable quart-sized bag OR 4 resealable sandwich bags (note: individual bags makes it easier to give out equal portions and the ice cream can be eaten right out of the bag with a spoon)
  • Oven mitts or gloves to keep your hands warm
  • Optional: spoons to eat your ice cream experiment
You should do this activity in the kitchen or a spot that is easy to clean up:
  • Mix the half & half, sugar, and vanilla in a bowl
  • For individual portions: pour 1/4 cup of the mixture into a sandwich bag and carefully seal the bag; then repeat 3 more times
  • OR – For one communal bag: pour all of the mixture into a quart-sized bag and carefully seal the bag
  • Put 2-4 cups of ice into the gallon-sized bag
  • Put the bag(s) of the half & half mixture into the gallon-sized bag
  • Put another 2-4 cups of ice into the gallon-sized bag
  • Sprinkle the salt on to the ice
  • Carefully seal the bag
  • Put on oven mitts / gloves
  • Shake and turnover the bag for 5 to 10 minutes and feel the cream mixture every couple of minutes to see if it has solidified
  • Take the bag(s) of ice cream out of the ice bag
  • Eat the ice cream with spoons (don’t try to eat it like a gogurt right out of the bag – the salty ice residue makes the outside of the bag super salty)
How did your liquid become a more solid ice cream? The basic answer is that the temperature of the mixture decreased enough for it to go from a liquid to freeze into a solid state. You might be surprised to know that the salt you added to the ice was critical to the process. For those of you that live through freezing cold winters, you’re probably familiar with salting your sidewalks and roads. Mixing salt with snow, ice, or other forms of water, actually decreases the freezing point – the temperature at which the water freezes.  When you added the salt to the ice, you reduced the freezing point which makes the salted ice bag several degrees below freezing.
Your ice cream mixture is in the middle of the salted ice and is brought down to the temperature of the salted ice. Since cream freezes and solidifies at a lower temperature, you get ice cream!
If you want to make this activity into more of an experiment, you can change a couple of components:
  • Do the experiment the same way, but don’t add salt to the ice – you could even do it first without the salt and then add the salt later when the half & half mixture doesn’t solidify if you’d like to conserve on bags and materials
  • Substitute milk or heavy cream for the half & half
You can find more information and options at ThoughtCo. and Scientific American. Let us know about your tasty findings!