In my opinion, there is no better sweet treat than ice cream on a hot summer day. My kids definitely agree and would eat ice cream all day everyday (probably in the winter too).
We’ve had our fair share of trips to the ice cream shop this summer, but I thought it would be fun to make ice cream at home with the kids and turn it into a STEAM activity too!
I saw an Instagram post about making ice cream in a bag from Systematic Motivation a few months ago and thought it was a great idea. We’re using her post as inspiration and a few Pintrest posts I found for the recipe in today’s experiment.
Our ice cream turned out great, and I know I’m going to have to keep lots of half-and-half on hand this summer because we are going to be making this a lot! I’ll get to the recipe and experiment soon, but first – the science!
Let’s talk about the STEAM concepts behind homemade ice cream
There are several STEAM principles involved in making this ice cream. In the science category there is a change of state and volume change due to bubbles involved, in the engineering category there is heat transfer, and in the math category there is measuring, counting, and adding ingredients.
I’ve talked about change of state several times on the blog, and I talked about it in most detail in my only other previous STEAM for Kids post that involved cooking: our Rice Krispies Treats experiment. If you like this post, I highly recommend checking out that post too! 🙂
Change of state happens when matter changes from liquid to gas or solid, and vise versa due to being heated or cooled. Water is always a great example because it changes state between liquid, solid and gas. Water is liquid at room temperature. If it is cooled to a temperature below freezing it becomes ice, a solid. If the ice is heated it will melt and change state back to a liquid, water. If the liquid water it is heated to above boiling point it changes steam, a gas. If the gas is cooled to room temperature it will condensate back to liquid water.
In this experiment heat transfer is occurring during our change of state. Ice absorbs energy in order to melt (this is an endothermic process). Heat is transferred from the cream solution to the ice, making the ice melt and the cream colder. Eventually as the ice absorbs more and more energy from the cream mixture it will begin to freeze.
This heat transfer is causing two changes of state: the ice is melting to become liquid water, and the cream mixture is freezing to become ice cream.
Salt lowers the freezing point of the ice. Since ice cream is not pure water (it contains fats and other ingredients), it needs a temperature lower than 32degF to freeze. Salt lowers the freezing point of ice from 32degF to 20degF in a 10% salt solution. Adding salt will make the ice take longer to melt, thus absorbing more energy from the ice cream mixture and freezing the mixture as it pulls away the heat.
The amount of salt added affects the quality of the ice cream. Too much salt can make the ice cream freeze too fast, causing it to be grainy, and too little salt can can make the ice cream freeze too slow, making it too soft.
Volume is the amount of space a three dimensional object occupies. In this experiment, when we make the ice cream the 1/2 cup liquid cream mixture turns into 1 cup of frozen ice cream. Why does the volume double?
The volume increases partially due to air being added into the mixture when we are tossing it around and shaking it. Also, when water (which is present in half-and-half) changes state from liquid to solid it expands due to the crystalline structure of the solid water molecule (think about when you put a full bottle of water in the freezer and it bursts or expands to the full limits of the bottle when frozen).
There are plenty of opportunities to practice basic math with your kids as you do this experiment. You can have your child help you measure and pour the ingredients into the bags. As you measure they will learn about the importance of accuracy in cooking and science, and how to read measurements on the measuring cup.
When adding ice to the gallon size bag, have your child count each cup as your add it into the bag to help them practice counting and adding skills. Keep adding until the gallon size bag is full and count how many cups it takes!
As you toss the bag around, try some math games. You can have them count how many times you can throw it back and forth with out dropping it! Keep going to see how high you can get (can you get to 20, 50, or 100?), starting over every time you drop it.
You can have a bag shaking competition. Count how many times each child can shake it before they need to stop. Who can do the most shakes at a time?
Vanilla Ice Cream in a Bag Recipe and Experiment
This is a fun summer (or anytime really…) STEAM activity for anyone from toddlers to adults. It’s simple, easy, fun, and delicious! You won’t be disappointed with this perfect summer treat.
Be sure to alway instruct your children to never put a plastic bag near their face, and especially never over their head. This is a suffocation hazard, so make sure you are observing young children at all times when you have empty plastic bags out.
The ice is very cold and prolonged exposure can cause freezer burn to your children’s hands. To avoid this, I recommend sharing the task of shaking the bag (each person only hold it for 30 seconds max), and using a towel and/or wearing gloves while handling the bag of ice.
- 1 Gallon size Ziplock freezer bag
- 1 Quart size Ziplock freezer bag
- 1/2 Cup half-and-half or whole milk
- 1 Tbs sugar
- 1 tsp vanilla extract
- 1/2 Cup salt (rock salt makes smoother ice cream)
- Ice (about 8-10 cups)
- Towel and/or gloves (optional, but recommended)
Note: It’s worth buying the brand-name Ziplock freezer bags for use in the experiment. They are stronger and more durable to hold up to the tossing and shaking involved to make the ice cream. I recommend double-bagging both the bags, because if the inner bag leaks, the ice cream is ruined (we’ve learned from experience!).
- Take out all your ingredients. Ask your child to form a hypothesis about this experiment. What will happen when we place these ingredients in a bag and shake it?
2. Add the half-and-half, sugar and vanilla (and any other flavors you like in your ice cream) to the quart size freezer bag, and tightly seal it.
3. Put the ice and salt inside the gallon size freezer bag.
4. Place the filled smaller bag inside the larger bag, and tightly seal the larger bag.
5. Vigorously shake and toss the bags for about 10 minutes, or until the ice cream is frozen. Try some of the counting games I described in the section above.
Remember, the bags have to be constantly moving the whole time for best results! We enjoyed tossing it around to each other, shaking it to the beat of music, and dancing with it.
On our first try we mostly tossed (and dropped) the bag. When it dropped it caused the outer bag and eventually the inner bag to leak, which ruined the ice cream.
6. Open the large bag and remove the smaller bag.
7. Dry the small bag (making sure to wipe off all salt, especially around the top so none gets into the ice cream)
8. Open the smaller bag and observe and discuss the change that happened to the ice cream (see discussion notes below in What Happened section).
9. Grab some spoons, dig in and enjoy your homemade ice cream!
You can eat it straight out of the bag or transfer to bowls to enjoy. We topped our vanilla ice cream with sprinkles. 🙂
The liquid half-and-half mixture changed state from liquid to solid, meanwhile the ice changed state from solid to liquid. Heat transfer occurred between the two substances – the ice melted because it absorbed energy from the cream mixture, turning the cream mixture into frozen ice cream.
You should have noticed that the volume of the ice cream is now close to 1 cup. The volume increased from 1/2 cream to 1 cup ice cream due to air bubbles being added as we tossed the bags around, and due to the ice crystals expanding as they formed in the ice cream.
We added salt to decrease the temperature at which the ice melts. The more salt you add, the faster the ice cream will freeze. But be careful, because if ice cream freezes too fast it is grainy. If it freezes too slow it will be soft. Try it making several batches with varying amounts of salt like they did on From Engineer To SAHM’s post.
This is a new family favorite activity for us that I am sure we will continue doing all summer long, and beyond! Nothing tastes better or is more fun than homemade ice cream that you get to shake and throw around in a bag to make!
Have you ever tried making homemade ice cream like this before? How did yours come out? Do you have any suggestions for tweaking the recipe or adding flavors?