Plastic bag ice cream is a delicious science experiment for kids. Not only can they learn to make their own dessert, but they can also learn about exothermic reactions and freezing-point depressions. The basic lesson is to teach kids that in order for the cream to freeze the temperature needs to be way below zero. The only way to do this is to get rid of some of the heat by transferring it to the rock salt used in the recipe. The end result is ice cream in a plastic bag!
Instructions
1. Seal 1/2 cup of milk, 1/2 tsp. of vanilla and 1 tbsp. of sugar in a quart-size zipper bag, making sure to squeeze out as much of the air you can so the bag doesn't open when you shake it.
2. Double bag the mixture to avoid leakage. Place the first bag into a second quart-size zipper bag, releasing as much air as possible before sealing it tightly.
3. Fill a gallon-size zipper bag with crushed ice and nestle the double-bagged milk-sugar mixture in the ice.
4. Sprinkle 4 tbsp. of rock salt on top of the ice. Though regular salt will also work, your ice cream won't be as solidly frozen. Rock salt is specifically designed to absorb heat and lower the freezing-point of water.
5. Seal the gallon bag tightly after letting out as much air as you can.
6. Put on plastic gloves to protect your hands from the cold or wrap the bag in a towel or old t-shirt.
7. Shake and gently squeeze the bag. You'll need to make sure that the inner bag is constantly surrounded by ice during this process.
8. Check the mixture about five minutes into shaking it. If it's not ice cream yet, it will be well on its way. Shake it a few minutes more if necessary, then open the bag over the sink.
9. Leave the bag with ice in the sink to finish melting and remove your ice cream.
Tags: quart-size zipper, your cream