Cows' milk, as well as that of most other mammals, is a complex mixture of proteins, fats, water, carbohydrates, minerals, hormones and various other molecules. Some of these components are soluble in water, others are suspended. The first step to making butter is to let cow's milk rest (or centrifuge it to speed up the process) until a lot of the fatty constituents have floated to the top. We call this layer the cream, and it is skimmed off, heated up and then cooled, to harden the fats. It’s at this point that the cream will be put into a churner, be it the wooden ones pioneers used, an industrial modern one, or a jury-rigged one made of a jar to be passed around a kindergarten classroom. The act of churning the cream, which is largely akin to shaking it around or stirring it, breaks up the lipoprotein membranes surround fat globules so that more and more globules of fat join together. Eventually, after a lot of churning, shaking or stirring, almost all the globules in the cream will have joined together to form the solid that we call butter. As the solid is disturbed further, the water contained in it will disperse throughout the butter in finer and finer drops, leading to ‘smoother’ seeming products. The liquid leftover still contains some fat, however, and is siphoned off to be used and sold as buttermilk.