Pasteurization is important because it kills harmful bacteria. Raw milk and dairy products can contain microorganisms such as Salmonella, E. coli and Listeria that cause food-borne illnesses.
Many health problems result from unpasteurized milk, such as tuberculosis, listeriosis, typhoid fever, diphtheria and brucellosis. Symptoms of illnesses caused by unpasteurized milk are vomiting, diarrhea, abdominal pain, fever, headaches and body aches. Women who contract the Listeria bacteria from unpasteurized milk while pregnant can have miscarriages.
The pasteurization process occurs when milk is heated to just below boiling temperatures. This process was invented by Louis Pasteur in the 1800s as a way to keep milk fresher longer. Two types of pasteurization are in use today. In the high-temperature, short-time treatment process, milk is run between metal plates and heated pipes for 15 seconds. Pasteurized milk, contrary to some claims, does not cause lactose intolerance or milk allergies and does not lessen nutritional value. It also does not last when stored outside of the refrigerator.
Although most milk and dairy products in the United States undergo pasteurization, there are some exceptions. Some soft cheeses use unpasteurized milk in the crafting process and can be harmful. These raw milk cheeses include Brie, Camembert, queso fresco, queso panela, asadero and queso blanco.