Instead, we took some knowledge from the recipe book of the ice cream ball (the heavier the cream, the faster it'll freeze) and combined it with this ice cream science activity from 3M. The ball recommended heavy cream for the fastest freeze time, and the 3M activity says 1 cup of milk or half and half would work. Personally, I didn't like the taste of all cream ice cream, and all cream would get expensive on the larger scale. I tried 50/50 this time, but I think I'll still like the taste better with even less cream (I'm a lighter ice cream gal) - so even more experimenting here before Science Saturday next month.
J's a little young to understand the lowering of the freezing point of water using salt. It doesn't help that we live in a place where it doesn't freeze, so we don't need to salt our sidewalks during winter time. I also wanted a 10 minute maximum for attention needed. The mixing of ingredients and change of matter is scientific enough for my four year old, and the fact that he gets ice cream at the end of it kept his attention fairly well (in fact, it made him pretty hyper).
Ice Cream Recipe (adapted from 3M activity)
1/2 cup heavy whipping cream
1/2 cup milk
1/2 tsp vanilla
2 T sugar
-Combine all ingredients into a quart sized zipped baggie. Zip the baggie, letting out all possible air.
-3M says to double bag the ice cream so we did (again with no air bubbles since air acts as insulation). I'm sure this is just so the ice doesn't accidentally puncture the ice cream mixture. I'll take extra precaution to ensure non-watery+salty ice cream.
-Place ice cream in a gallon sized zipped baggie full of 4 cups of crushed ice and 1/2 cup of rock salt. Zip the gallon baggie, and 3M says to gently shake. J got a little excited with the shaking that by no means was it gentle.
We set a timer for 10 minutes and started shaking the baggie around on squishing/mixing the ice cream with our hands. However, after a minute or two, the ice + salt got too cold for our sensitive hands. Instead of reaching for our "winter gloves" which I just thought about, John grabbed a towel and wrapped the ice cream + ice in the towel. We tossed it around that way for a few minutes. We combined it with punching/kneading the baggie through the towel.
The timer dinged after 10 minutes and the ice cream was perfect! It was enough to even split between J and me. Despite our cold hands setback, this method was actually easier and less to clean up than the ice cream ball. All we had to do was toss the bags - no dishes other than the few measuring devices and the bowls we transferred the ice cream to. You could enjoy the ice cream right out of the baggie instead of bowls.
|The seal of approval|
|One satisfied scientist|
Discussion for younger kids:
*What ingredients are you mixing together? What if you vary the ingredients (ie the ratio of milk to cream or additives like cookie pieces or chocolate chips)? Do you think it will work the same? How do you think it will taste?
*Is the ice cream mixture solid, liquid, or gas when you mix it together? What about when it becomes ice cream?
*Is ice hot or cold? When we stick something in ice does it get hotter or colder? What about the ice; does it get hotter or colder?
*What happens if we just stick the ice cream mixture in the freezer? How long will it take to freeze? Does it taste the same as the ice cream you made in your baggie?
Add on discussion points for older kids:
*What did the salt do to the ice? Why did the salt melt the ice?
*Get a thermometer and measure the temperature of the ice cream mixture, the ice before adding salt, the ice immediately after adding ice, the ice cream after it freezes, the ice + salt mixture after the experiment is over. What did you observe? What's the freezing point of water? Is the ice + salt mixture below the freezing point of water?
All in all, baggie ice cream was a success, and I do think ice cream making would be feasible for the next Science Saturday. Tentatively, we're scheduling it for Saturday, July 13th (of course we depend on weather and family wellness). Shoot me an email if you want specific details. Hope to see you then!
*Baggie ice cream follow-up: temperatures of ice+salt.
*Science Saturday in the park: ingredients needed for 30 kids.
*Make ice cream in a ball