Make ice cream in a bag – Quick and tasty STEM activity

Making ice cream in a bag from start to finish.

Did you know you can make delicious ice cream really quickly with just a few simple ingredients and a bit of science? This simple STEM experiment doesn’t require any fancy equipment and is a fun way to combine cooling down on a warm day with some hands-on science.

Ice cream making through the ages

Ice cream has been enjoyed as a luxurious treat for centuries. Initially, the process was elaborate and labour-intensive, especially before the invention of modern refrigerators and freezers. Ice was often harvested from frozen lakes or ponds and then mixed with salt to create a brine solution that could freeze the cream in special pots or churns. While not precisely the same method, this experiment nods to those times gone by and explores some of the science behind ice cream making.

Before you get started

This guide will show you how to make ice cream in a bag in around 25 minutes from start to finish. The difficulty level is pretty easy, but here are a few extra tips to help ensure your experiment runs as smoothly as possible:

Preparation space

This activity has the potential to get a bit messy, so work on an easily cleanable surface and consider wipeable or throwaway table coverings to protect surfaces.

Safety

As we’re dealing with food, hygiene should be a priority. All surfaces and utensils should be clean, and hands should be washed thoroughly before and after. We highly recommend that an adult be present and actively supervising at all times.

Ingredients

We used half double cream and half whole milk for our ice cream mixture. The activity can be carried out using just milk, but the texture won’t be quite the same. The double cream gives a delicious creamy taste!

Here’s a list of what you’ll need for your ice cream in a bag:

  • 180ml Double cream
  • 180ml Whole milk
  • 3 tbsp Sugar
  • Vanilla extract/essence
  • 2 resealable food bags 
  • Ice cubes
  • Half cup of salt (we used table salt)

This recipe makes enough for two good sized portions. If your bags are on the smaller side, you might want to try halving the recipe as you should avoid over-filling the bags.

Ingredients list for ice cream in a bag experiment.

Note that vanilla extract and essence are different, so adjust the amount you put in according to the recommendations on the packaging. We used about half a teaspoon of vanilla extract in this recipe.

The bags

Use good quality, strong freezer bags. As you’ll be shaking/massaging bags containing liquids, double check the bags to ensure they are completely sealed to prevent any leaks.

Ensure the bags are large enough to easily hold your mixture without being too full.

If you can, use a larger bag for the ice and salt mixture, as this will make mixing them easier.

Timings

Whilst we’ve estimated a total project time of 25 minutes from start to finish, this can vary quite a bit depending on a few factors. These include how vigorously the bag gets shaken, the temperature of your ingredients, how much ice/salt you use, and the ambient temperature of your room. It can be a fun exercise to try the experiment a few times to see if you can beat your time.

Cleaning up

Have a towel, cloth or paper towels handy in case of spillages! Also, remember to completely wipe off the excess salty water from the bag containing the ice cream before it’s opened.

How to make (almost) instant ice cream in a bag

The following steps detail how we made our ice cream.

Prepare your mixture – Carefully add your milk, cream, sugar and vanilla extract to one of the bags. Ensure there’s not too much air trapped in the bag and seal it tightly. Then give it a little massage to mix the ingredients.

Mixing the ingredients in the bag.

Prepare the ice bath – Fill the second bag about half way with ice cubes and add the salt.

Ice cubes in a bag

Combine the bags – Place the bag with the mixture carefully inside the bag with the ice and salt. Make sure it is tightly sealed before moving on to the next step.

Combining the bags.

The exciting part! – Shake and massage the bag for around 5-10 minutes or until the mixture thickens into ice cream. The bag’s contents will get VERY cold, so use a towel or gloves for this step.

Shake the bag.

Serving your homemade ice cream – Remove the smaller bag and completely wipe off any saltwater (you don’t want any of this to mix with your ice cream). Carefully discard the salt water from the other bag without spilling it.

Serve the ice cream.

Finally, scoop the ice cream from the bag and serve it in a bowl. Add any toppings you like – we used sprinkles for ours. Getting all of the ice cream from the bag can be tricky, so you might want to cut it open so that it can all be scooped out with a spoon. Enjoy!

Adding salt to the ice might seem like a strange thing to do, but it plays a crucial role in the process. Adding salt to ice lowers the freezing point of water, a process known as freezing point depression. This allows our ice and salt mixture, now called brine, to remain liquid even below 0°C (32°F). This very cold liquid can chill our ice cream mixture very quickly.

While we shake the bags, the salt and ice mixture pulls heat away from the cream, milk, and sugar mixture, helping it to freeze into ice cream by turning the liquid mixture into a solid..

Why not try experimenting with different flavours and toppings? Use flavoured milk instead of plain milk, or add crushed cookies or candy pieces after the ice cream has formed. See what imaginative new flavour combinations you can come up with!

Wrapping up

We hope you enjoyed this activity as much as we did. The first time we tried this, we were genuinely surprised at just how delicious and creamy the end result was. If you liked this, be sure to check out some of our other hands-on activities too.

Happy churning!

Read more about the history of ice cream in this article from the British Museum.