Erin Steiner, age 11, of White Plains, N.Y., for her 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.

Pasteurization 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: They heat milk to at least 161 degrees for at least 15 seconds and then cool it.

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