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.com, 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."
