Science Activity: Making the Coolest Ice Cream

1. Get Ready    

Two sandwich-sized, zipper-top plastic bags
Two gallon-sized (3.7 liter), zipper-top plastic bags
1 cup (about 250 milliliters) very cold chocolate milk
2 tablespoons sugar
1/2 teaspoon vanilla flavoring
Coarse salt (Available in large supermarkets and hardware stores. You may use rock salt as long as it's pure sodium chloride.)
About 6 quarts (6 liters) miniature ice cubes, crushed ice, or regular ice cubes
Measuring spoons and cups
Plastic spoon for tasting
Watch or clock

2. Do and Wonder

Original Ice Cream

To make the ice cream mixture, add the following to the sandwich bag: 1 tablespoon sugar, 1/2 cup (about 125 milliliters) chocolate milk, and 1/4 teaspoon vanilla flavoring. Seal the bag tightly, and then shake it to mix the contents together.

Next prepare your ice cream freezer. Add the following to the gallon (3.7 liter) bag: 2 tablespoons of coarse salt and enough crushed ice, miniature ice cubes, or regular ice cubes to fill the bag between half and three-fourths full. Seal the bag tightly, and shake it to mix the ice and salt.

Set the small, sealed bag with the ice cream mixture into the center of the large, sealed bag with the ice and salt mixture. Write down the time.

Shake the small bag and turn it over and over until you can see that the ice cream has hardened. (This will take at least 15 minutes.) When you're sure the ice cream is firm, write down the time.

Remove the ice cream from the bag and taste it. Observe its flavor and texture.

Your Improved Ice Cream

Now create your own brand of ice cream by changing the recipe and the procedure you used for freezing it. For example, maybe add different flavorings and ingredients to the ice cream mixture and more or less salt to the ice and salt mixture.

How long did it take your improved ice cream to freeze? How does it taste? What's the texture like?

3. Think and Write

In a short paragraph, compare the taste of the original ice cream with the taste of your improved brand. Also compare the textures and freezing times of the two ice creams. Finally, describe what else you might do to improve the taste and texture of your ice cream.

Explanation    

The freezing temperature of water is 32 degrees Fahrenheit (or 0 degrees Celsius). Adding salt to water lowers its freezing temperature. When salt is placed on ice, a reaction occurs that moves some energy from the environment to the ice, causing it to melt. Anything near the melting ice loses some of its heat energy and gets colder. In making ice cream, the liquid ice cream mixture gets colder and harder.

Safety Hint    

Don't use any other salt-containing products besides coarse table salt or rock salt that's pure sodium chloride. Other ice­-melting products contain chemicals that are unsafe to handle and should never be used near food.