Making Ice Cream
Making Ice Cream
What could be a better science project in the summer than one you can eat?
On TV we made the process a little quicker because we didn't have 20 minutes or so, but there are plenty of ways to make ice cream and take up time for your kids. Here are two ways to do it.
Put your favorite recipe for ice cream (ours is below) in a 1 quart ziploc style bag. Put that bag inside a 1 gallon ziplock style bag. Put ice and rock salt in the outer bag. You might want to surround the outer bag with a towel so your hands don't get cold. Move the bag around to try to make the ice cream in the inner bag freeze evenly. It should take about 20 minutes. We have a link to a site that tells more about this method below.
Put your favorite ice cream recipe (ours is below) inside a 1 pound coffee can (thoroughly washed if you don't want coffee flavored ice cream). Put on the cover and place the 1 pound coffee can inside a 3 pound coffee can. Put in a layer of ice followed by a layer of rock salt, followed by a layer of ice, etc., until the outer coffee can is full. Put on the lid of the outer coffee can. Roll the two coffee can apparatus around on the floor (or the patio) for about 20 minutes and the ice cream should freeze.
We like the way that we make ice cream on TV or in chemistry shows, but it's not one that people can do at home. It's still a cool experiment, both literally and figurtively. We make our ice cream from the following recipe.
This recipe is enough to make a good helping of ice cream for about 20 people.
We use 4 L beakers made out of Nalgene for the actual freezing of the ice cream. The beakers we use were purchased just for making liquid nitrogen ice cream and have never been used in a laboratory. In other locations I have used glass (Pyrex) beakers and stainless steel pots, so it is possible to do other things. We like the beaker because it makes it look more scientific, but the pot looks more Shakespearean, so you can take your pick if you are planning to do the demonstration.
Liquid nitrogen is very cold, so it is the dangerous part of this demonstration. We have had one accident in the past where a student making the ice cream spilled a bit of liquid nitrogen on her shirt. It might have been around 40-50 mL, but it soaked into the shirt, was held against her skin, and let to a nasty burn.
To freeze the whole batch will probably require about 1.5 to 2 L of liquid nitrogen. Pour it in at a modest pace and stir well to try to avoid getting ice crystals. When we do this demonstrations on TV we use a small portion of the recipe and pour a little more quickly so we get the ice cream frozen quickly enough for the short TV time slots. In any even - it's good tasting chemistry with a great show to boot!
Making Ice Cream with ZipLock syle bags - a site from about.com
Making Ice Cream with ZipLock style bags - a site from inmamaskitchen.com
Making Ice Cream with Coffee cans - a site from childfun.com