This is a special method of applying a mild degree of heat to milk and other liquids for destroying undesirable and harmful nonspore- forming microbes. It is really not a process of sterilization, but rather of disinfection. It was originated by Louis Pasteur and used by him for killing micro-organisms which cause undesirable fermentations in the process of making wine.
Pasteurization is now extensively used for freeing milk from disease germs. The process of pasteurization of milk consists of heating it to 60°-65°C, (140°-150°F.) for one half hour, followed by a rapid cooling.
In most modern dairies the raw milk is carried in pipes from large receiving tanks to the pasteurization machines. Just before entering these machines, it is passed through hot pipes which warm it to the pasteurizing temperature.
The pasteurizers consist essentially of tanks in which the milk held at the necessary temperature (usually 142°F is used) and continuously stirred for half an hour. Then the milk passes through long cold pipes, in which it is rapidly cooled, and from these pipes is carried to automatic bottling and capping machines.
As we have already learned, this heating destroys the vegetative forms of practically all bacteria, including those of any disease germs that may be present.
The milk is not sterilized-pasteurized, milk sour, though more slowly and in manner somewhat different than unheated milk-but all pathogenic bacteria or viruses likely to be found in it are killed.
Pasteurization does not appreciably alter the quality or flavour of milk, although its property of preventing scurvy is somewhat diminished. Infants need the antiscorbutic principle, but this is readily supplied from odier foods, and boiled or pasteurized milk is the only proper kind of milk for them.
Pasteurization of milk is encouraged by health authorities everywhere and is required by law in many localities, for it is one of the most important measures for the public health.