Always wear eye protection during science experiments. Never handle sharp objects, open flames, chemicals, or other dangerous objects without adult permission and supervision.
We usually don't think about it, but cooking really is science! In this demonstration, we're going see how butter, a solid, can be separated out of cream, a liquid, simply by shaking.
To figure out why this works, let's think about what cream looks like on a molecular level. Cream is what is known as a colloid, a type of mixture where particles of a substance are not dissolved, but suspended evenly throughout another. In the case of cream, microscopic blobs of butterfat float around in a watery liquid called whey. Other colloids you might know are milk (also butterfat in whey), mayonnaise (oil in vinegar), and even whipped cream (air in cream--two colloids in one!).
In order to make butter from cream, we have to separate the butterfat blobs from the whey. Heavy cream has such a high butterfat content that, by churning or shaking the cream, we can force the microscopic fat blobs to bump into each other, gradually forming bigger and bigger blobs, sort of like a snowball rolling down a hill. And hopefully, after all this shaking, we'll end up with some whey and one big blob of butterfat--butter!
Pour the heavy cream into the container and make sure that the lid is on tight.
Shake the cream inside the container until the whey begins to separate from the butterfat. This can take a while and a lot of elbow grease, so it's a good idea to have someone to take turns with. We also recommend doing the shaking over the sink or in an area that can afford to get messy (just in case).
Every few minutes, stop shaking and try peeking into the container to observe what's happening to the cream. Can you see both the butter and the whey?
After shaking the container for a while, you might notice that it no longer feels like you're shaking only a liquid, but that something is flopping around inside the container. Take another peek and, if at this point the butter is completely separate from the whey, you're all done! At this point you can pour out the whey and taste your scientific butter. Feel free to add a little bit of salt to make your butter taste even better.