The raw milk, regardless of what type of fluid product it’s destined to end up as, passes through a separator which spins the milk through a series of conical disks. This removes debris, sediment and some bacteria. But it also separates out the fat, splitting the contents into a cream portion that is 40 percent fat, and skim milk that is less than 0.01 percent fat.
The skim milk is drained away, then, has precise quantities of fat returned back to it, or not, depending on whether it’s going to remain as skim milk, or become 1 percent, 2 percent, or whole milk which contains between 3.25 percent and 3.4 percent milk fat based on the processor’s formula.