The Role of Pasteurization

by Nina Planck

Commercial dairies, industrial cheese makers, and distributors prefer pasteurized milk for practical reasons. Pasteurization permits more handling and long-distance shipping. On most commercial dairies, the farmer pours milk into a refrigerated bulk tank after each milking. Every few days, a truck comes to collect the farmer's raw milk. The milk from many farms and thousands of cows is blended together in the truck and bottling plant. 'The risk of contamination-which only takes one diseased cow or dirty udder-is too great,' writes Harold McGee in On Food and Cooking. Though it is not fail-safe, pasteurization can prevent a batch of contaminated milk from one unhealthy cow or dirty nozzle from tainting the clean milk from hundreds of cows.

Another practical benefit of pasteurization for the dairy industry is longer storage. Standard pasteurization extends the shelf life of milk from one week to two or three weeks. Ultra-pasteurized milk keeps for more than eight weeks. Aseptic UHT milk does not need to be refrigerated at all and can last for ten months.

Food preservation has a long and noble history. Some traditional foods, such as honey, wine, and cheese, are designed to keep. Raw milk, however, is not one of them. Here's a wise rule of thumb: Eat foods that will spoil-but eat them before they do.

For all its benefits, pasteurization is not perfect. In practice, pasteurization can have an unsavory effect on hygiene. It allows less scrupulous dairy farmers to be lax with animal health and milk handling. They count on pasteurization to destroy pathogens-at least the heat-sensitive ones-that may have contaminated milk. Inspection of dairy herds for disease is not required for milk destined for pasteurization. On dairy farms licensed to sell raw milk, herds are tested regularly.

Nor is pasteurization a guarantee against food poisoning. Listeria, for example, can survive at temperatures of 150 degrees Fahrenheit-hotter than gentle pasteurization. Moreover, both raw and pasteurized milk can carry pathogens. Pasteurized milk may be contaminated at any point-during handling, transport, storage, or cheese making. Many cases of pasteurized milk and cheese tainted by Listeria, salmonella, and campylobacter have been reported.

It is striking that outbreaks of diseases such as salmonella have risen steadily since pasteurization became standard. No one is certain why. Salmonella and E. coli do thrive under the conditions typical in factory farms, including grain-feeding, crowding, and rapid, mechanized slaughter. Overuse of antibiotics on factory farms has also led to resistance to common antibiotics in strains of salmonella, campylobacter, and E. coli. Whatever the reason, the rise of these food-borne pathogens cannot be blamed on raw milk. The sequence is backward.