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Have you ever wondered how ice cream is made? We know it involves a base mixture getting cold enough to solidify into the tasty treat, but how can we make that happen without an ice-cream machine to simultaneously whip and freeze the mixture?
To make ice cream by hand, we need to remove heat from the base mixture so it can solidify, which means it needs to drop below 32 degrees Fahrenheit (0 degrees Celsius).
In this activity, we will be making ice cream by hand using our own muscle power to churn the ice cream and ice to freeze it into a creamy solid. But we also need something to lower the freezing point of our ice (which is normally 32 degrees Fahrenheit) to make this delicious dessert.
That secret ingredient is salt.
Ever heard of roads getting salted in the winter? Roads are treated with salt because it can keep roads from icing over. When salt is added to ice, it lowers the freezing temperature of the ice, allowing it to melt at normal freezing temperatures – meaning the roads are cold and wet but not icy when they hit freezing temperatures of 32 degrees Fahrenheit or lower.
Now, for the ice-cream!
The interaction between salt and ice is important in this tasty science activity so that we can get our mixture to below-freezing temperatures to solidify. When we churn our ice cream mixture within a bag of ice and salt, the mixture cools down and begins to solidify, and after some time, becomes a delicious summer (or anytime) treat!
This activity will take about 5 minutes to prepare and approximately 10-15 minutes of learning time. It is best suited for children in elementary school.
- Gallon sealable bag (not slider bags)
- Quart sealable bag (not slider bags)
- Measuring spoons
- Measuring cups
- Rock salt (rock salt works best for a smooth texture; mix will be chunkier if using table salt)
- Milk (or milk alternative), half and half or cream (if you are making the ice cream base)
- Vanilla extract or flavored syrups (if you are making the ice cream base)
- Fruit juice (if you are making sorbet)
- Fruit toppings (if you are making sorbet)
- Make your base in the quart-size bag. For ice-cream, mix together 1 cup of milk base, 1 tsp. vanilla extract and 2-3 Tbsp. sugar (or 2 Tbsp syrup flavoring in place of the vanilla and sugar). For sorbet, add 1 cup fruit juice and 2 Tbsp. fruit toppings.
- Seal the bag really well and shake to mix ingredients together.
- Fill your gallon-size bag about a third of the way with ice.
- Pour ½ cup of rock salt onto the ice.
- Place your sealed quart-size bag with your base mixture in the gallon-size bag and seal.
- Wrap your gallon bag in a towel and start shaking. Twist, flip, shake your bag for about 5-15 minutes. It will get very cold so keep it wrapped in the towel. Check on it every few minutes to see if it is the consistency you want for your frozen treat.
- Remove the quart bag from the gallon bag and wipe off the outside.
- Grab a spoon and dig into your homemade dessert!