Sweet Chemistry! | Boys & Girls Clubs Of Ada County

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.

Pretty cool!