Kids and Colonial re-enactment players know that when you shake heavy cream vigorously, you get butter. (The cream must be at room temperature or warmer for best results.) The chemical processes that lead to the butter-making can be a little complex at first. The key to understanding what happens to cream when shaken is the butterfat. How the butterfat reacts to the shaking is just as important.
About the Cream
Cream is the thick white portion of the whole milk that rises to the top when the milk settles. Although it comes from whole milk, cream contains a higher percentage of fat than whole milk. Whole milk is 3.25 percent butterfat. The rest of the whole milk is made up of water. Cream, however, is 35 percent butterfat and 65 percent water. This heavy fat content is what makes cream the only dairy product from which butter (made up of 80 percent fat and 20 percent water) can be made.
How It Works
When the cream is shaken in a jar or container, the fat molecules in the cream collide. As they hit one another, the molecules stick together, forming a growing lump of butterfat. The molecules collect until most of the fat in the cream has joined the large ball of fat in the center of the liquid. Some people stop shaking before this occurs, which results in small balls of butter.
That leftover liquid is not useless. It is, in fact, another important cooking ingredient -- buttermilk. It is the milky white liquid that has the fat removed in the form of butter. The tangy leftover liquid is used in making quick breads and batter to fry chicken or chops. Place the buttermilk is an airtight container and then in the refrigerator until you plan to use it.
After you have finished shaking the butter from the cream, and have stowed away the buttermilk, it is time to finish the butter. Put the butter in a medium-size mixing bowl (smaller for small balls of butter). Sprinkle a pinch of salt on the butter ball and mix it in. The salt enhances the flavor of the butter and act as a preservative to prevent spoilage for up to two weeks. Scoop the butter into an airtight storage container and keep it in the refrigerator until you need it.