Hey kids! Here’s a simple recipe you can follow right at home to make your own ice cream, and do a science experiment at the same time!
Ice cream in a plastic bag is made by lowering the freezing point of ice, so the ice can freeze the ingredients. The scientific secret ingredient is plain old salt!
You’ll make the ice cream by surrounding the ingredients with a layer of ice cubes. When you add salt to the ice, the chemistry forces the ice cubes to melt. (That’s why salt is used on icy roads and sidewalks in the winter.) When salt and ice mix, the freezing point of ice is actually lowered and as it melts, it borrows heat from the surrounding objects. This is called an ENDOTHERMIC process. Since your ice cream ingredients aren’t as cold as the ice, the ice borrows heat from the ingredients and makes them freeze up into ice cream. Science never tasted so good!
You will need
• 1 cup (8 ounces) half-and-half (or 4 ounces of milk and 4 ounces of cream)
• 1 tsp of vanilla (or use other flavors usually found near the vanilla in a grocery store – you can use chocolate syrup for chocolate ice cream)
• 4 tsp of sugar
• A few drops of food coloring (optional – if you want colorful ice cream)
• Lots of ice (at least 4 cups)
• Lots (half cup) of salt. Rock salt (sold at hardware stores) works best, but you can also use kosher salt.
• Small (quart size) zip freezer bag
• Large (gallon size) zip freezer bag
What to do
1. Put the milk, cream, flavoring, coloring, and sugar into the SMALL quart-sized zip-bag and zip it shut (be sure to seal it tight, get the air out, and close it completely)
2. Add the ice and rock salt to the LARGE gallon-sized zip bag. Shake it around to coat the ice with the salt
3. Put the small bag with your ingredients into the larger bag so that the ice completely surrounds it.
4. Zip the large bag shut (be sure it is zipped) and then carefully hold opposite sides of the bag and SHAKE, SHAKE, SHAKE the bag back and forth for about 5-8 minutes. You can wrap the bag in a towel so it’s not too cold to hold.
5. Open the larger bag and take out the smaller bag – it should be full of ice cream! Rinse off the bag under running water to remove any salt that may be near the opening of the bag.
6. Open by snipping off the corner of the bag and squeezing your ice cream into a bowl.
By Karen Rice