Introduction: How to Make Ice Cream in a Bag

Have you ever wondered about the science behind making ice-cream? Well now you can combine the experience of creating an awesome dessert with the satisfaction of learning cool chemistry principles. In this experiment we will be making “ice-cream in a bag” by using rock salt to drop the temperature of ice to the freezing point of milk. This experiment is geared for any age, and is a great thing to do with friends and family. It would be especially good for a college student to do in a club meeting, as well as for younger kids to follow instructions and complete so they learn about freezing point and chemical reactions. If you have an allergy or lactose intolerance, you can accommodate for these allergies by using a lactaid milk instead of regular milk, or subbing toppings like nuts for something like fresh fruit.

The project can completed anywhere you have access to the necessary ingredients, but a suggested place is in a room with lots of space, where you will complete the reaction by shaking the bags over a large bowl that’s sitting on the table. This will allow any water that escapes from the ice melting to be contained in the bowl, as well as to have a contained space for shaking the bags to create the ice-cream.

Step 1: Ingredients

  • quart sized ziploc bag
  • gallon sized ziploc bag
  • rock salt
  • ice
  • 1/2 cup of milk or heavy whipping cream
  • 1 tablespoon of sugar
  • 1/4 teaspoon of vanilla extract
  • extra toppings
    • for example, you can add fruit, nuts, crushed oreos, or chocolate syrup

Step 2: Fill the Bigger Bag

Here is where we begin mixing our supplies together.

First, fill the large, gallon sized bag with the ice you prepared as well as rock salt.

Step 3: Fill the Smaller Bag

Next, fill the smaller, quart sized bag with the milk or heavy whipping cream, sugar, vanilla extract, and any other toppings you’ve chosen to use. Here I added peaches and oreos.

Step 4: Release the Air

Before beginning the freezing step, you’ll want to make sure to let out all of the excess air inside the smaller bag. It should look like the bag above.

Step 5: Place the Smaller Bag in the Bigger Bag

Now place the smaller bag inside of the bigger bag and release the air from that as well.

Step 6: Let's Get Shakin'!

Once we have the bags set up, the only thing left to do is shake! It is necessary to continue shaking until your ice cream reaches your desired texture. The longer you shake it, the firmer your ice cream becomes. This is what mine looks like.

Step 7: (Optional) Try Again With More Ice!

This was the result of my second attempt with more ice and more shaking.

Step 8: Congratulate Yourself!

Since you have reached this point, congratulations! You now know how to make ice cream from scratch! Next time, you can now add new toppings, try different milks, and experiment with new flavors.

You are now an “ice-cream-ologist”! Not only can you make a homemade sweet treat for yourself, but you can also explain the chemical principles involved in making a delicious bowl of ice-cream!