Science Lessons From Making Freezer Bag Ice Cream

Before we made the ice cream we did some experiments. First, we took two glasses of water and put the rock salt into one of the glasses. The glasses went into the freezer and every 15 minutes we checked to see what happened. It’s pretty fun to see kids get so interested in the simplest things. He needed to really examine the glasses of water and observe how it was freezing. We talked about how salt is used to melt ice and how salt water freezes at a much lower temperature. Why is salt used to make ice cream? It allows the temperature of the mixture around the ice cream to get colder. You can read more about the science of freezing salt water here. The glass on the left is fully frozen after one hour while the glass on the right with salt water is kind of slushy.

Then I had him get another glass with a little water and dish soap. I gave him a straw and told him to blow bubbles. He had a lot of fun making a bubbling mountain. We talked about what was happening. The volume had expanded, it was flowing out of the glass and into the sink. Why? We had added air and vibration. I explained to him that is what we would do with the ice cream. By shaking and throwing the ice cream ingredients we would be adding air and vibration so the final product would have more volume than what we started with. (A 1/2 cup of half and half will make 1 cup of ice cream.) The bubbles were really engaging for him. I wanted to go off on a tangent and explore the science of bubbles but I left that for another day.

Introduce the children to the three stages of matter. Matter can move from one state to another, but can still be the same substance. Not everything can change from one matter to another. For example, a diamond is always solid. Have the kids think about things that can change their stages of matter, like snow and chocolate. The faster the molecules move determines the stage of matter. Temperature affects how fast the molecules move. Gas has the fastest moving molecules and solids the slowest. You can demonstrate the process by melting ice cube and heating them until you make steam.

Finally, it was time to make ice cream! Like I said before, I want to add lessons while we are having fun. I made a scientific method worksheet for him to record our experiment. He gave it the title of Making Ice Cream. It amused me when he wrote his hypothesis: “The half and half will not turn into ice cream.” After he had written the materials and procedure it was time to actually make the ice cream.

To make Freezer Bag Ice Cream you will need:

• Small freezer bag
• Large freezer bag
• 1/2 cup of half and half
• 1 TBS sugar
• 1 tsp vanilla
• 1/2 cup of rock salt (our store called it “ice cream salt”)
• Crushed Ice

Instructions for making Freezer Bag Ice Cream:

• Put the half and half, vanilla and sugar into the small bag. I use two bags just in case one breaks.
• Put the smaller bag(s) into the larger bag. Again I double up the bags because they usually break.
• Put the ice and salt into the bigger bag.
• Shake, smash, throw until the half and half has frozen and become ice cream. Stop and take some time to observe what is happening.
• Measure how much ice cream you have. Is it more than the 1/2 cup that you started with? Why?

• Use cream instead of half and half. Is there a difference? Why?
• Use almond milk instead of half and half. Is there a difference? Why? (Hint: the fat content makes a difference.)

By the time that we were done my young friend had learned many science lessons from making Freezer Bag Ice Cream but in his mind, he had just had a fun time playing and eating a delicious cool treat.