Some bacteria are normally present in the udder of the cow, and these may contribute to the bacterial flora of the milk. However, unless the udder is infected, it is not considered to be an important source of such microorganisms.
In addition of udder, the exterior of the udder, the bedding on which the cow lies, food eaten by the cow, the milker (hands, nose and throat), the air in milking barn, water used to wash the udder, and milking and storage equipment are considered to be the source of bacteria.
In the handling of milk upon delivery to the processing plant or dairy, further sources of contamination may be encountered.
The hairs of the cow are always covered with dirt and dust and it is impossible for the milker to avoid a considerable amount do this dirt falling into his milk pail. Every one of these hairs which finds its way into the milk will furnish large quantities of bacteria for contamination.
Cows suffering from disease like salmonellosis, tuberculosis, and brucellosis may shed the bacteria that cause these diseases onto their milk.
In order to limit the number of bacteria present in raw milk, certain precautionary procedures are ordinarily applied. The flanks, udder, and teats of the cow should be washed, treated with a sanitizing solution, and dried before milk is drawn. Large dairy farms often have a special wash pen for cows to be milk.
It is essential to cool the fresh milk as quickly as possible. The temperature to which milk can be cooled on the farm will depend on the facilities available.
If mechanical refrigeration is available then the milk can be cooled to 3 - 5 °F and the frequency of delivery to the processing plant need no more than three times a week.
Utensils, including the milking machine, should be cleansed and disinfected either with live steam or with a solution of chlorine (about 200 ppm of available chlorine). Bulk milk tanks may be cleaned manually with detergent and water at about 54.5 °C, the sanitized with chlorine solution, or cleaned mechanically with detergent and water at 65.5° C, and finally sanitized with chlorine solution.
Outlet valves and the outside of the tanks must be cleaned and sanitized manually. Cleaning in place (CIP) may be used to clean, sanitized, and rinse the pipe line and the bulk milk line tank of a vacuum or pressure system is available.
Source of bacteria in milk
