Most of the dairies today provide pasteurisezd milk to the consumers. At east, the claim to do so. When you a milk which is pasteurized, you are sure that you are drinking safe mik.
Pasteurized milk is milk which has been heat-treated to kill pathogens which cause disease. Not all pathogens are removed during the pasteurization process, so pasteurized milk is not 100% sterile, but many people consider it to be safer to drink than raw milk which has not been pasteurized at all. The bulk of the milk sold in commercial grocery stores is pasteurized, and much of it is also homogenized to prevent the cream from separating.
The pasteurization process is named for Louis Pasteur, a noted French microbiologist. Pasteur made a number of notable discoveries in the field of microbiology, developing techniques which are still used today to reduce the risk of disease. In 1862, he performed early pasteurization tests, determined to render milk safe to drink, and the practice was adopted very quickly. Before pasteurization, improperly handled and stored milk caused widespread disease, especially in urban areas, where several unrefrigerated days might elapse between the cow and the end consumer.
There are several different pasteurization techniques which can be used to make pasteurized milk. The goal of pasteurization is to render the milk safe to drink without curdling or coagulating it, and without altering the flavor substantially, although people who are accustomed to drinking unpasteurized milk may find that pasteurized milk has an “off” flavor.
In high temperature/short time (HTST) pasteurization, the milk is brought to a temperature of 161 degrees Fahrenheit (71.7 degrees Celsius) and held there for 15 to 30 seconds before being rapidly cooled and packaged. Double pasteurization splits the process up into two segments, and is not recognized as a legal pasteurization method by some governments. Extended shelf life (ESL) milk is pasteurized at a slightly lower temperature and passed through a special filter to remove microbes. Ultra high temperature (UHT) pasteurization involves bringing the milk to 250 degrees Fahrenheit (138 degrees Celsius) for less than a second, while batch pasteurization is performed at a very low temperatur=e, with the milk being held to temperature for 30 minutes before being cooled.
Even after pasteurization, milk is not totally stable. It will go bad within two to three weeks under refrigeration, with the exception of UHT milk, which can be held at room temperature in aseptic packaging for up to three months. Pasteurization also doesn't eliminate the risk of contamination along the supply line, as for instance in the case of pasteurized milk which is pumped through contaminated piping, and it doesn't eliminate heat-resistant organisms, although it does get rid of many common pathogens.
The benefit of pasteurization is that it renders milk much safer to drink. However, it also destroys some of the enzymes present in the milk, including enzymes which make milk easier to digest. It also alters the flavor of the milk, although people who are accustomed to pasteurized milk may not be aware of the difference between fresh raw milk and pasteurized milk. As a result of these drawbacks, some people prefer raw milk, despite its dangers.
When a cow is milked, and as the milk settles, a layer of cream forms at the top of the milk. This used to be the way people would judge the quality of milk. A thicker layer of cream meant better quality milk, and especially when milk was still normally sold in bottles, you could easily see into the bottle to judge the cream layer.
Homogenized Milk-The next Step
Pasteurization had become standardized for milk in most countries, since heating the milk destroys any bacteria in it, making the milk safer to drink. Homogenized milk was the next step. Pasteurized milk could still easily have milk fat proteins separate from the rest of the milk. For some people this was viewed as a disadvantage, though others argue homogenized milk doesn't taste as good.
Since milk is an oil and water combination, it doesn't stay mixed. Homogenized milk is run through tiny tubes, sometimes during the pasteurization process to keep fat and liquid molecules together. Fat molecules are reduced in size and tend to disperse more evenly throughout the milk so that creaming on the top of milk doesn't occur. You can also use the homogenization process to reduce overall milkfat in milk. 2% milk is stripped of some of the fat molecules to produce lower fat milk
Homogenized milk also helps deal with a side effect of pasteurization. When milk is heated, the white cells and bacteria collect on the bottom of the milk, forming a thick, and many think, disagreeable layer. When milk has been fed thorough a small tube or orifice, this bottom layer gets mixed through the milk. The process of making homogenized milk, which gained the most popularity in the 1950s, has resulted in longer lasting milk, and the ability to ship milk greater distances.
Not everyone is pleased with homogenized milk, and sometimes you can look for unhomogenized versions. These still may be pasteurized, but many come in raw milk versions, which can prove unsafe to drink. Though it must be said that many people drink raw milk with no ill effects, there is occasional bacterial contamination of raw milk that poses a potential health risk.
However, there are debates going on with the homogenized milk as studies point out it has ill-effects.
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