Raw Milk Facts, a website advocating raw milk consumption, wrote in an article titled "Homogenization: A Closer Look" (accessed Dec. 10, 2007):

“Homogenization today is usually a two step process. The first stage…pushes milk through small, tapered tubes or pores. As the diameter shrinks and the flow of milk remains constant, pressure builds up and fat globules break apart in the turbulence.

The higher the pressure, the smaller the particles. How much pressure? Typically 2,000-3,000 pounds per square inch (psi), although some super homogenizers work at over 1000 times atmospheric pressure- 14,500psi and higher!

You can jam milk through pretty small holes with force like that. Before homogenization, fat globules range in size from 1-10 microns (a micron = ~0.00004 inch). After, the size range is reduced to 0.2-2 microns.

As the much smaller fat globules begin to reassemble, they include fragments of whey and casein in their walls. Some are completely surrounded by a layer of protein. The tendency is for these new, chemically altered globules to clump together. Stage two of the homogenization process breaks up this unwanted assembly and makes sure everything stays in solution.”

Dec. 10, 2007