On a microscopic level, butter is fascinating stuff. It’s been called an “inside out” emulsion since it starts out as dispersion of fat globules in a continuous phase of water (cream) and ends up as a dispersion of water droplets in a continuous phase of fat (butter). Pretty funny, eh?
I said pretty funny, eh???
(Sound of crickets chirping.)
Ehem. So how does this miracle happen? Well it all starts with preparing the cream. The first thing that happens is it’s pasteurized, i.e. heated to 185 or so degrees Fahrenheit. After that the cream is slowly cooled to about 40, at which point something very interesting happens: fat crystals start to form in the mixture. This is an important step for the ultimate texture of the butter, which depends on a careful balance of fat crystals and “free” liquid fat. Too many crystals and the butter will be brittle, too few and the butter will leak liquid fat and be overly soft and “greasy.”
Next step, the churning, whereby the mixture of fat crystals, fat globules and water is agitated. Though it seems simple enough, the process is actually quite complicated, so much so that it’s still not completely understood. Essentially what happens is this: brittle fat crystals puncture the membranes of the fat globules, which spill out their “free” fat molecules into the mixture. That free fat flows together and around the crystals forming a continuous mass. At the same time much of the water is pushed out (this water, which contains a small amount of fat plus other flotsam, notably the membranes of the fat globules, is known as buttermilk).
The final step is “working” where the butter is essentially kneaded to squeeze out any last pockets of buttermilk and bring it to an even consistency. Once that’s done it’s ready to packaged and sold. Cool, yes? Yes???