To avoid creaming and prevent contaminating microbe growth that will acidify the milk and potentially cause disease, raw milk is quickly shipped to local processing centers where raw milk is homogenized and pasteurized. These are two different processes that allow milk to be stored, shipped, and safely consumed long after milking the cow. Homogenization is a process that breaks the milk fat globules into much smaller and more uniformly sized fat globules. Fresh from the cow, milk fat globules range from 1 to 10microns (μm); after homogenization the globules range from 0.2 to 2.0μm in diameter.
Milk is homogenized as raw milk is forced at pressure through very small diameter nozzles. Large milk globules are forced through a narrow opening, which causes the membranes to sheer, essentially breaking the tough globules coverings while mixing together and creating many smaller fat globules. The result of homogenization is the many smaller globules whose fat droplets are only partially covered by membranes.
The exposed lipid droplets quickly become covered with casein proteins from the liquid phase of the milk. All of this results in smaller, casein‐coated milk fat globules that are less likely to separate from the rest of the milk. The negative charge from the casein proteins ensures that the milk fat globules do not combine and form a solid layer of fat. Pasteurization is the process of quickly heating and then cooling the milk.