Jessica Samson, age 12, of Lansing, Mich., for her question:

WHO FIRST THOUGHT OF PASTEURIZATION?

Preserving food by heat and cold is called pasteurization. It is used most commonly for milk but is also used for cheese and other food.

A French chemist named Louis Pasteur invented the process in 1865.

Modern dairies pasteurize milk by heating it to 161 degrees Fahrenheit for about 15 seconds and then cooling it quickly. Pasteur's method was to heat the milk to 145 degrees for not less than 30 minutes and then to chill it quickly to 50 degrees. With both methods it is necessary to keep the milk cold until used.

Pasteurization keeps germs from multiplying rapidly but does not greatly affect the flavor of milk or food.