Cool kitchen science: Handmade ice cream

Give your first- or second-grader a beginner's lesson in chemistry with a favorite, frozen childhood treat.

By Sarah Henry

Food is a fantastic teaching tool. Children can learn about math, chemistry, nutrition, biology, culture, history — you name it — all while playing with something that's both tactile and tasty.

And since eating is an everyday activity, food-related exercises help kids explore their environment through a medium that's fun and familiar. Adults can pass on their values about food, stress the importance of eating wholesomely, and encourage kids to learn to cook dishes they love as well as try something new as part of an edible education. The activity that follows can be adapted for any age group. Enjoy!

The project: Discover ice-cream chemistry

What could make that summertime staple ice cream even cooler to your first- or second-grader? The science behind shaking and making a liquid into a sweet, creamy solid.

Explain to your child that when freezing the liquid ice-cream mixture, ice keeps things cold because it absorbs heat energy from its surroundings in order to melt, changing from a solid to liquid. Adding salt to the ice lowers the freezing point of the ice so that even more heat energy has to be absorbed from the surroundings (in this case, the ice-cream mixture) for the ice to melt. When enough heat has been removed from the liquid mixture, it freezes and becomes a solid. The larger salt crystals take more time to dissolve in the water around the ice, which allows for even cooling of the ice cream.

What you’ll need

1 cup milk or half-and-half
2 tablespoons sugar • ½ teaspoon vanilla extract
½ cup rock salt or ice-cream salt (the bigger the crystals the better)
3-4 cups ice cubes
1 pint-size Ziploc bag
1 gallon-size Ziploc bag
Spoon and cup measures
Optional: chocolate chips, sprinkles, or berries

Make it happen

Measure the sugar, milk, and vanilla extract in the smaller bag and seal well.
Place the salt and ice in the gallon-size bag.
Place the sealed smaller bag inside the bag with the salt and ice.
Seal the larger bag well. Now roll or shake the bags as you count to 100. Look at the mixture. Do you see a change?
Keep shaking, counting, and observing for about five minutes. You may want to wrap the bag in a dishtowel so that your hands don't get too cold.
The mixture should start to harden, so squeeze it every few minutes to check if it's ready.
When ice cream forms, take the small bag out of the larger one, add desired toppings, and enjoy eating the results.

GreatSchools tip

Ask your child to jot down beforehand what he thinks will happen and why. As you eat the ice cream, discuss what happens when the temperature of something changes and it can't hold its shape, introducing the concept of liquids and solids.

Sarah Henry is a Bay Area-based freelance food writer and the voice behind the blog Lettuce Eat Kale.