Submitted by: Lindsay Blaser
Ice cream is a summer staple, but most of us don’t really understand how simple ingredients like cream, sugar, and vanilla combine to form this delicious treat. Not so for our teens who enjoyed a chemistry lesson with some sweet results. Specifically, we made ice cream.
Behold: The Chemistry of Ice Cream
Essentially, ice cream is just a combination of three ingredients: milk, sugar, and flavoring. However, simply mixing these ingredients and putting them in the freezer would NOT yield ice cream! Instead you would just have a solid block of sweet frozen milk. In order to achieve ice cream, you must churn the ingredients while freezing to aerate or incorporate air and create a creamy texture. This process also helps to emulsify the mixture, distribute the sugar and flavor evenly, and form ice crystals within the mixture.
The formation of these ice crystals has to happen in a very particular way, otherwise you just end up with frozen milk. This is why it is important to use whole milk or heavy cream to make the ice cream. The fat in the milk helps to keep the ice crystals that form from getting too large. The sugar in the mixture actually lowers the freezing point of the water which also reduces the amount of ice formed by the freezing process.
In lieu of a traditional churn, we used zip-top bags. combining all the ingredients in a small baggie, and then placing that inside a larger baggie filled with ice mimics the results of an old hand-crank ice cream churn. Just filling a bag with ice is not cold enough to freeze the ice cream, especially on a hot summer day! For that we need to provide another chemical reaction. By adding salt to the ice, we lower the freezing/melting point of the ice which allows it to remain at a sub zero temperature even as it melts.
Ice Cream in a Bag Recipe!
- 1⁄2 cup half-and-half
- 1 tablespoon sugar
- 1⁄4 teaspoon vanilla
- 1 sandwich zip-top bag
- 1-gallon zip-top bag
- 3 cups crushed ice
- 1⁄3 cup rock salt
- Combine the first 3 ingredients in the small baggie and seal. Make sure it is tight! Put the ice and rock salt in the larger bag, then put the smaller bag in the larger bag. Seal the bag and shake the whole thing until the ice cream has thickened (about 10-15 minutes). Unseal, grab a spoon, and enjoy!