Ann Stanley, age 11, of Windsor, Ontario, Canada, for her question:
WHY IS MILK PASTEURIZED?
Almost all of the milk sold in the United States is pasteurized. Pasteurization involves heating the milk to a high temperature. The procedure is followed so that any disease causing bacteria that might be in the milk will be killed.
Most milk is pasteurized by the high temperature method, which is also called the short time method. This process requires the milk to be heated to more than 161 degrees Fahrenheit for at least 15 seconds and then immediately cooled.
Some milk is pasteurized by the low temperature method, which is also called the holding method. This routine requires that the milk be heated to at least 145 degrees Fahrenheit for 30 minutes or longer and then cooled.
Still other milk, and other dairy products such as whipped cream, are pasteurized by the ultrahigh 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.
Even though there are a number of different methods used, pasteurization has only one purpose: to kill any disease causing bacteria that may be in the milk.
Pasteurization is used chiefly for milk but may also be used for cheese, beer and other food products.
A French chemist name'd Louis Pasteur invented the process in the mid 1800s.
Pasteur discovered that bacteria in food multiply rapidly and cause the food to spoil. Ordinary boiling will kill all bacteria, but the heat of boiling destroys the flavor of milk.
Pasteur found that boiling the milk is not necessary, that most of the bacteria are killed with less heat than boiling, and if the milk is chilled after being heated, the bacteria do not multiply again rapidly.
A man named Nathan Straus was a pioneer in the campaign for pasteurization laws in the United States. '
As soon as a tank truck of milk arrives at a processing plant, laboratory technicians check the odor, taste and appearance of the milk. They also measure the fat content, the number of bacteria, the amount of milk solids and the acidity.
Technicians further test the milk during and after processing. All this testing helps ensure the quality and purity of the milk. Milk is the most highly tested of all foods.
After the first test, the milk is pumped into a large refrigerator storage tank. On the way to the tank, it passes through a clarifier that removes any hair, dust or similar matter from the milk.
Then, in order, come separation, pasteurization, homogenization, fortification.