Well Summer Scientists, depending on the part of the country you are currently in you may be feeling the heat right about now. That is why I decided that the best thing for us to do next was make fresh, delicious, FROSTY ice cream from scratch. As a bonus, this ice cream can be used to make Root Beer floats with the homemade root beer you made last week!
Now, my twist on this activity comes from my high school Chemistry class, taught by Dr. F. Instead of making the ice cream in a pair of plastic baggies, we are going to make it in Coffee Cans! Why you ask? Well, two reasons. 1) As the ice cream is freezing that baggie gets C O L D… and so do your hands! Way colder than I like them to be personally. The coffee cans will also get cold but it’s not as big of a deal because 2) they ROLL! You don’t have to touch them very much because you set them to rolling back and forth (find a friend!) which can be pretty darn fun! Let’s get started!
What You Need:
- 1-1lb. Coffee Can
- 1-3lbs. Coffee Can
- Box of Rock Salt
- Crushed Ice (Sonic Ice works great)
- Ingredients for your favorite Ice Cream Recipe (here are some No-Cook no egg recipes, and HERE are recipes for those of you who like to live more dangerously and include eggs or dont mind cooking the mix a bit)
How Its Done:
- Clean out your 1lb. Coffee Can thoroughly. Nobody wants old coffee grinds in their ice cream. Unless you do, and then I guess that is a personal decision.
- Pour all of your ice cream ingredients into the 1lb. can (note: if you are using a more complicated recipe, complete all the steps prior to putting the mixture in the ice cream maker, then dump it in the can)
- Put a lid on that baby. Make sure it is sealed up tight. If your ingredients aren’t already fully mixed, give it a little shake until it is. Shoot, give it a little shake even if it already was, it’s fun!
- Place your little can in your big can, and fill the big can about 1/3 of the way with crushed ice. Sprinkle a generous layer of rock salt on the ice. Continue layering ice and rock salt until the 3lbs. can is full. Seal her up!!
- Grab a buddy and stand about 4 feet away from each other. Roll (or kick) the can(s) to each other for about 10 minutes. Be careful not to kick it too hard.
- Check the ice cream – if it is not add more ice and salt and roll again for another 8 minutes. It should be frozen at this point, but if not, more ice and salt!
- Once it is frozen, scoop into bowls and Enjoy!
What is going on here??
Ice cream is an interesting creature in that it is both an emulsion (fat droplets suspended in another liquid; a trait shared by milk, mayonnaise, and salad dressing) and a foam. The combination of proteins and fats in the mixture help to stabilize the structure, and when made correctly the ice cream will have a smooth, creamy consistency. Technically, the thing that stabilizes the emulsion is called an emulsifier. In foods the emulsifier is usually egg yolk, honey, or mustard.
Mixing the right combination of ingredients together isn’t enough to make this frozen delicious treat though, as you probably know. In order to achieve the temperatures necessary to freeze our mixture, we added rock salt to ice. If you live somewhere where it snows or ices over during the winter, you may be familiar with the concept of salting streets and driveways. As it happens, the salt and ice combine to form a brine (salt-water) which has a much lower freezing point than pure water. In fact, the more salt you add, the lower the freezing point will be! The coldest temperature can be achieved by making a 20% salt solution – it freezes at -20°C (that is -4°F in America ;))
As you add the salt to the ice they mix to form the salt water, which begins to melt. Now it may seem like opposite day when I say this, but as in order for the ice to melt, it actually has to ABSORB energy from its surroundings in order to heat up, which actually makes the area around it colder. This is the principle behind why ice makes our drinks nice and chilly. The heat leaves the beverage (or in this case, the ice cream mixture) and enters the ice to melt it. Since the melting point of the salty ice is so much lower than pure ice, this allows our ice cream to solidify. Yay!
This activity is a great way to see chemistry in action – plus you get a delicious summery treat out of it! Enjoy 🙂 and don’t forget to tell us what flavors you made!