Video narration
Why does a cream layer rise to the top of a bottle of milk, while homogenized milk stays evenly mixed? Untreated milk has larger fat globules, tiny droplets of fat, that slowly move upward and gather into that visible cream layer. Follow it into a homogenizer, a machine that forces milk through a very narrow valve at high pressure. The machine does not dissolve or remove the fat. As milk rushes through, pressure suddenly drops. Turbulent flow and shear-sliding forces-stretch and disrupt the large globules into many much smaller droplets. The total fat remains; only the droplet size and distribution change, not the fat itself. Milk proteins help keep those droplets apart. Because the new droplets are smaller, they rise far more slowly, so the cream layer does not quickly return, and the milk stays evenly mixed longer.