I am admittedly too young to remember the days when milkmen used to bring fresh bottles to the door a couple of times a week—but I’ve heard the stories. People always tout the freshness of the milk and reminisce about how you would have to shake the bottle to mix in the cream. Milk delivery may not be as ubiquitous as it once was, but that doesn’t explain why we no longer have to shake our milk.
The answer to this quandary is actually quite simple: the homogenizer. The cream, or fat, portion of the milk has a lower density, so it naturally rises to the top of the bottle. A homogenizer works to break down the fat molecules so that they can be mixed into the rest of the milk, creating aptly named “homogenized milk.”