Birthdays are great opportunities to celebrate the wonders of science!
• Heavy cream (1 cup)
• Ice (enough to fill a 1-gallon bag)
• Milk, whole (1 cup)
• Optional: flavor add-ins, such as chocolate chips, chocolate syrup, chopped strawberries, or crumbled cookies
• Resealable plastic bags, sandwich-size (2) and gallon-size (2)
• Salt, kosher or rock (1/2 cup)
• Sugar (1/2 cup)
• Vanilla extract (1 tablespoon)
- Prepare the ice cream bag — measure and add the heavy cream, sugar, vanilla, whole milk, and flavor add-ins of your choice to a sandwich-size resealable plastic bag. Push out the air and seal it tight. Double bag it to be safe!
- Prepare the ice and salt bag — fill a gallon-size resealable plastic bag halfway with ice and pour the salt on top.
- Place the ice cream bag inside the ice and salt bag. Seal it tightly.
- Shake the bag for about 5-10 minutes while singing your favorite songs.
- Observe how the contents of the bag change in appearance, temperature, shape, and texture as you shake.
- Add ice to another resealable gallon-size plastic bag and compare the way it feels to the ice and salt bag. Which one feels colder?
- Unseal the ice and salt bag, remove the ice cream bag, and enjoy your treat!
The Science Behind It
The ice and salt bag should feel colder than the bag of ice without any salt. Also, you may have noticed that the ice in the ice and salt bag melted more than the ice in the bag without salt. Why? Salt disrupts the formation of ice crystals and lowers the freezing point of the ice. When the freezing point is lowered, the ice needs to absorb more energy in order to melt. This results in the temperature of the ice and salt mixture dropping below freezing while also absorbing heat from the surroundings and melting the ice. Liquids conduct heat better than solids, so the super-chilled ice water is able to lower the temperature of the sugary milk and cream mixture faster than ice alone ever could. This process turns the mixture into a solid, creamy treat. Be sure to share the sweetness of science with your friends!