Simple (and Scientific) Homemade Ice Cream

Our family doesn't currently own a car so all of our travel is done via our own two feet, biking, and the occasional bus ride. On really hot days this causes us to ravenously burst through the door in search of cold stuff to shove into our mouths.

I came across this fantastic recipe for homemade ice cream last year. We have enjoyed it several times both as a family and in our Science Kiddo classes. The thing I like the most about about this ice cream is that you don't need any special equipment or ingredients to make it. Plus, it is a delicious and refreshing way to learn some science!

To make any variety of homemade ice cream you need to partially freeze your milk or cream. Water freezes at 32°F, but because milk contains proteins and fat it freezes at a lower temperature. This means that trying to freeze milk with ice cubes won't work. You need to add a special ingredient to your ice cubes to make a mixture that is colder even than ice alone. Ready for the secret ingredient? I'll give you a few clues. It's white. It's something almost everyone has in their kitchen. It tastes yummy on popcorn with butter. It's....SALT!

We talked about the magical science of how salt and ice cubes work when we did our Fishing for Ice experiment and when we made our delicious fruity slush. When you add salt to ice, it lowers the freezing point of the ice, making it melt. You are left with a salty-icy-watery mixture that is much colder than 32°F. The temperature of your salty mixture is close to 0°F! (You can verify this with a thermometer.) This temperature is cold enough to freeze milk, thus enabling you to enjoy yummy homemade ice cream in less than 10 minutes. Put it atop your morning waffle if you so desire.

Total Time: 10 minutes or less

Difficulty: The one trick with this experiment is making sure you don't contaminate your ice cream mixture with your salty water. This leads to yuckiness.

Materials You Need:

One small Ziploc baggie (quart or sandwich size)
1/2 C. milk (whole works best, but any variety will be fine)
1 Tbsp. sugar
1/4 tsp. vanilla

One gallon-size Ziploc bag
8-10 C. Ice
6 Tbsp. salt

Directions:

• Add milk, sugar, and vanilla to the small baggie. Seal the bag, being careful to release excess air.
• Add ice and salt to the bigger baggie.
• Place the small baggie into the large bag of ice and salt. Seal the large bag.
• Shake for about 5 minutes or until the milk mixture turns into a soft solid.
• This is the tricky part: Open up the large bag, remove the small bag and rinse it off quickly in cold water (pay special attention to rinsing off the opening). You don't want any of the salt water getting into your sweet and creamy ice cream!
• Either grab a spoon and eat your ice cream right out of the bag, or pour your ice cream into a bowl. Either way, eat it and enjoy!

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