Mary Hembrey, age 13, of Austin, Tex., for her question:
HOW IS MILK PASTEURIZED?
Almost all milk sold in the United States today is pasteurized by a high temperature, or short time, method. Pasteurization involves heating the milk to kill disease causing bacteria that might be in it. Pasteurization also helps to prevent or arrest the fermentation in some products.
The short time method of pasteurization requires milk to be heated to more than 161 degrees Fahrenheit for at least 15 seconds and then to cool it very quickly.
Some milk is pasteurized by the low temperature, or holding method. Such milk is heated to at least 145 degrees for 30 minutes or longer and then cooled.
Other milk and such products as whipped cream are pasteurized by the ultra high temperature method. This process requires a temperature of 280 degrees Fahrenheit or higher for two or more seconds. This method greatly increases the time a product may be stored before it spoils.
Louis Pasteur is the name of the French doctor who discovered that bacteria in food multiplied quickly and caused food to spoil. He found that boiling milk was not necessary since most of the microorganisms were killed with less heat than that required for boiling.
Pasteur, who is regarded as one of the world's greatest scientists, also discovered that bacteria do not multiply again rapidly if the milk is quickly chilled and then kept cold.
Almost all the whole milk and low fat milk sold in the United States is also homogenized. Homogenization breaks up the fat globules in milk so that the globules do not rise to the top.
A machine called a homogenizer forces the milk through tiny openings under great pressure. The process increases the number of fat globules and gives every drop of milk the same amount of cream. Such milk tastes richer than non homogenized milk.
Doctors and nutrition experts disagree on exactly how much or how little milk a person should drink.
Fortification improves the food value of milk by adding certain nutrients, especially vitamins and proteins. Most dairies today add Vitamin D.
Often skim milk is fortified with Vitamin A, as well as with Vitamin D. The reason for this is that skim milk loses much of its Vitamin A content when the fat is removed.
Dairies also increase the protein content of skim milk. A few dairies increase the amount of other vitamins and some of the minerals in milk.
Every state in the United States and every Canadian province produces milk in large amounts.
In the U.S., a large part of the industry is concentrated in the "dairy belt" which extends from New York to Minnesota. Wisconsin leads states in milk production, followed by California, New York, Minnesota, Pennsylvania, Michigan, Ohio and Iowa.
Quebec and Ontario are the chief milk producing Canadian provinces.