Joseph Tumminia, Jr., age 16, of St. Louis, Mo., for his question:

WHAT IS THE DIFFERENCE BETWEEN PASTEURIZATION AND HOMOGENIZATION?

Pasteurization is a method of preserving food by heat and cold. It is most commonly used for milk, but may also be used for cheese, beer and other foods.

Pastuerization consists of heating milk to at least 145 degrees Fahrenheit for not less than 30 minutes and then chilling it quickly to 50 degrees or less. Modern dairies now use a faster method: Milk is heated to at least 161 degrees for at least 15 seconds and then „.s cooled.

Homogenization is the breaking up of particles in an emulsion so that they are small enough not to separate. Milk is an emulsion of butter fat in water. To prevent separation, milk is forced through a narrow opening at high pressure. This breaks the large globules into small ones.