Science Experiment: Let’s Make Ice Cream!

July 16, 2023 |
By: Casey Vreeken

Have you ever wondered why salt is a key ingredient in making homemade ice cream? It’s not just for flavor! Salt plays a crucial role in freezing, allowing us to create that deliciously creamy treat. In this blog, we’ll explore the science behind why we need salt to make ice cream and guide you through a fun and educational activity to see this process in action. Ultimately, you’ll have a delicious, cool, and yummy treat to enjoy on those hot summer days!

IMG 2055 - Steamboat Studio

First, let’s gather our supplies for a cool experiment to understand the magic of salt and ice:

  • Cup
  • Ice
  • Water 
  • Thermometer
  • 2 tbsp Salt
  • Stir stick

Directions:

  1. Take the cup and add ice until it is ⅔ full. Use the thermometer to take the temperature of the ice. The ice should read as below freezing, since there is no liquid water with it, yet.
  2. Add water to the ice until the cup is ¾ full. Place the thermometer in the ice water and note the temperature. Leave the thermometer in the cup and start a 4-minute timer. At the 1 minute mark, take the temperature of the water/ice mixture without removing the thermometer. Repeat for minutes 2, 3, and 4.
  3. What did you observe? Hopefully you saw the temperature drop to approximately 32 degrees F and stay there. Depending on the quality of the thermometers you’re using, results may vary. There also may be some variation if you removed the thermometer from the ice water to read it.
  4. Add the salt as you start the next 4-minute timer. Continue to leave the thermometer in the mixture. Stir the mixture with a stirring stick – reminder, DO NOT stir with the thermometer. Repeat the process of taking temperatures for the next 4 minutes.
  5. You should see the temperature begin to drop again as the salt dissolves. Salt water has a lower melting/freezing point than plain water. Salt can be used on icy roads or sidewalks to lower the melting point of the ice. This causes the ice on the surface to melt making it safer for cars and people. 

Now for the fun part! Let’s make some ice cream.

Supplies:

  • Cup (at least 12 oz)
  • 1 cup Whole milk (or milk alternative)
  • 1 tsp Sugar
  • ¼ tsp Vanilla
  • stir stick
  • sandwich and gallon size bags
  • ½ cup ice cream salt
  • 2 cups ice
  • Spoon

In the first activity we saw that when salt is added to ice water, the freezing point is lower and it can reach temperatures below the freezing point of water. If we use plain ice water to make ice cream, the temperature will not get below freezing and will not freeze the ice cream mixture. By adding salt to the ice water the freezing point is lower and can reach temperatures below the freezing point of water and will allow the ice cream mixture to freeze.

Directions:

  1. Place a sandwich sized Ziplock bag inside a cup and add the ice cream ingredients to the bag: 1 cup milk, 1 tsp sugar and ¼ tsp vanilla 
  2. Mix with a spoon to dissolve sugar
  3. Carefully remove bag and seal bag with as little air inside as possible
  4. Place two cups of ice, ½ cup ice cream salt and the salty ice water from the previous activity in a gallon Ziplock bag
  5. Place milk bag in gallon bag, removing as much air as possible and seal
  6. Use your hands to gently agitate the milk bag inside ice water for 10-15 minutes until it solidifies.
  7. Once the ice cream freezes, remove the inner bag, wipe off any excess salt water from the bag before opening and enjoying your ice cream!

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