The Importance of Pumps In The Milk Homogenizing Process
Simply put, milk is a combination of proteins, fats, and water. When unhomogenized milk sits for any length of time, the fat will float to the top, creating a layer of cream. Homogenized milk has been mechanically treated to break up the fat globules so that they are smaller and more uniform in size. These smaller fat globules tend to stay suspended in the liquid rather than rising to the top. Homogenization is so common in the United States that labeling assumes it has been homogenized—milk has to be specially labeled if it has not been homogenized.
Homogenization is frequently done after pasteurization. This is because the enzyme lipase, which is deactivated by heat during the pasteurization process, can begin to digest the ruptured fat globules. If this occurs, it can lead to the milk becoming rancid.
Pumps play an integral part in the standard homogenization process that takes place at many dairies. At the outset, milk is pumped into a large drum or barrel where it is agitated. If the homogenization process is directly following pasteurization, the milk is generally warm. If it is not, heat is often applied at this stage as well.
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In the next step of the process, milk is pumped at high pressure through small holes. The high pressure forces the milk through holes small enough to break up the fat globules. How much pressure are we talking about? Homogenizers use pressures from 2,000 psi (pounds per square inch) to over 14,500 psi in some super homogenizers.
With forces that strong, you can force milk through some pretty small holes. Before homogenization, fat globules range in size from 1-10 microns. A micron is approximately .00004 of an inch. Once homogenized, fat globules are reduced in size to .2-2 microns.
The homogenized milk is pumped into storage containers until it is either bottled or transported. In the U.S., customer preference is one reason dairies often homogenize their milk. On large dairies, this process helps to blend milk from different herds more easily. Milk from different herds can have slightly different chemical makeups that hinder mixture without the homogenization process.
Homogenized milk also has a longer shelf life, which means that it can be transported greater distances. This means that large-scale dairies can do business with buyers who are located farther away. The homogenized product also lasts longer for the consumer. Separated milk must usually be consumed within a few days of being opened, while homogenized milk will generally last for a week or more.
One last benefit of the homogenization of milk is that it allows for a more precise creation of products with different levels of fat content, like 1%, 2%, and nonfat milk.
Milk homogenizers have become a staple of most U.S. dairies.