Science Craft: Ice Cream in a Bag

The summer has started and the library is awash with children. Tuesdays have traditionally been craft days for school aged children during the summer, with the crafts following the theme of the Summer Reading Program. This year’s Fizz, Boom, Read theme means I chose crafts that are at least marginally related to science. Sometimes this means that I had to stretch exactly what a “craft” is, but we’re making it work.

Our very first Tuesday Craft was Ice Cream in a Baggie. If you’ve never done this before, believe me, it’s worth it! The kids were thrilled about the ice cream and the parents were fascinated. I could tell that some of the adults were skeptical that it was going to work, and then amazed when it did. The kids, of course, never doubted for a moment.

Before we started I gave a little talk about how ice forms, using some of the children as volunteer water molecules. I then explained the effect salt has on ice, and how using salt lowers the freezing point, creating an even colder icewater solution. This is the key to making ice cream in a baggie.

So how does it work? First you get a big gallon sized baggie and put in ice and salt. I hadn’t thought to measure the ice and salt the way that I measured the ice cream ingredients, but no one had any problems, so apparently there’s a lot of leeway. I’d say the average child used a little less than two cups of ice and maybe a half cup of salt or less. Kosher or rock salt or the salt you can buy for ice cream makers are best, but table salt is much cheaper and works just as well. We used table salt without any problems.

Next you get a smaller baggie, pint or quart size. Into this second bag you put 1/2 C of whole milk (you can also use cream or half and half, but milk is cheaper when you’re buying for large crowds), a splash of vanilla (I had the children use the 1/8 tsp), and sugar. Because I had more measuring cups than I had measuring spoons I had them put in “a little less than 1/4 C” which made for some very sweet ice cream. In ideal circumstances I probably would have used about 2TB of sugar. But none of the children complained that their ice cream was too sweet, imagine that!

Next you seal the small baggie. Then check to make sure it’s sealed. Then triple check to make sure it’s really, definitely, absolutely sealed. After that you pop the small bag into the larger bag, close the larger bag, and shake, shake, shake. I’d intended to sing some shaking songs, but the noise of dozens and dozens of shaking bags was so loud that I didn’t even try. It takes about five minutes of shaking (and there were a lot of parents who ended up doing the shaking, so thanks parents!) and then the solution turns to ice cream! It’s a softish ice cream and a little grainy (using cream would have helped smooth it out) but delicious nonetheless.

While I did not add any flavorings other than vanilla, I have done this activity in the past with other flavorings. It’s easy to add a squirt of syrups intended for flavoring milk. If you want to add more solid flavors, such as strawberries or broken up oreos (my two favorites) then you need to freeze those additions ahead of time or the ice cream won’t freeze properly.

No pictures today because I was too busy running the craft.

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