Pasteurized milk has been heated and held at a given temperature for a certain length of time. This can be accomplished in two ways. The milk may be heated to about 143 degrees Fahrenheit and held at that temperature for thirty minutes, or it may be heated to 160 degrees Fahrenheit and held for about sixteen seconds. The process destroys most microorganisms and spares the flavor of the milk which higher temperatures would affect. The same process is also applied to wines.
Microorganisms, too small to be seen without a microscope, are the cause of tuberculosis, typhoid fever, dysentery, undulant fever, diphtheria, scarlet fever, and septic sore throat. Pasteurization prevents the spread of disease through the milk supply.
Pasteurization does not kill all the microorganisms present in milk. Many bacteria still live, but these are not harmful to the body. Milk is tested from samples taken from each source. The city or county health department is responsible for this task, and milk is graded according to the bacteria count and number of coloform organisms in each milliliter.
Unpasteurized milk may still be sold in some communities, but it must be used more quickly than milk which is pasteurized. Almost all milk sold in stores is Grade A pasteurized. Lower grades of milk are used in making powdered milk or cheeses as the bacteria will be destroyed by cooking or
chemical treatment.
