Dairy Farming Today, an organization that provides information about dairy production, provided the following information about homogenization in its article "Farm to Fridge" published on its website (accessed Dec. 10, 2007):
"Homogenization is a process that gives milk its rich, white color and smooth texture. Milk that has not been homogenized contains a layer of cream that rises to the top of a glass.
Before the homogenization process was used, milk was shaken or mixed to achieve consistency in its look and taste. The homogenization process involves reducing the size of the fat globules into miniscule portions that are dispersed evenly throughout the milk. Homogenization usually is achieved by pumping milk through small openings under very high pressure."
Douglas Goff, PhD, Professor of Dairy Science and Technology Education at the University of Guelph, Canada, wrote in a 1995 article titled "Homogenization of Milk and Milk Products," posted on the Dairy Science and Technology website:
"Milk is an oil-in-water emulsion, with the fat globules dispersed in a continuous skim milk phase. If raw milk were left to stand, however, the fat would rise and form a cream layer. Homogenization is a mechanical treatment of the fat globules in milk brought about by passing milk under high pressure through a tiny orifice, which results in a decrease in the average diameter and an increase in number and surface area, of the fat globules. The net result, from a practical view, is a much reduced tendency for creaming of fat globules."
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."