STEM Lab: Make Ice Cream in a Bag in Just 15 Minutes

☀️ A Cool Snacktivity for a Hot Summer Day

By Tatiana Sayig, publisher of Macaroni Kid Five Towns-Valley Stream-The Rockaways, N.Y. June 1, 2020

I love when you can combine science with a delicious edible treat.

So I was excited to find a STEM activity that involved making ice cream in a bag. It seems like magic, but there is real science happening inside the bag! The salt and ice make a solution that gets cold enough to freeze your milk.

The recipe below for ice cream in a bag makes two small servings. Want more? Double your ingredients. This makes vanilla ice cream, but add some powdered chocolate and you have chocolate ice cream! Experiment with other ingredients to make other flavors!

What You Need:

  • 1 cup any kind of milk or half-and-half
  • 2 Tbsp. sugar
  • 1/2 tsp. vanilla extract
  • 3 cups (doesn't need to be exact) of ice
  • 1/3 cup salt
  • One sandwich-sized plastic resealable bag
  • One gallon-sized plastic resealable bag
  • Gloves

What You Do:

  1. Mix milk, sugar, and vanilla in the small bag. Squeeze out the air and seal.
  2. Mix ice and salt in the large plastic bag.
  3. Place the small bag into the big bag.
  4. Shake hard for 5-7 minutes or until the milk mixture is frozen. Use gloves because the bag will get very cold!
  5. Grab a spoon and enjoy!

The Science Behind the Fun:

When salt comes into contact with ice, the freezing point of the ice is lowered. Water will normally freeze at 32˚F. Ice cream needs to be frozen to a temperature less than 32˚F and the salt makes that possible.

Try This: What happens if you add less salt, more salt, or no salt?