Ynte Schukken, professor of epidemiology and herd health, poses with livestock.

Will a fresh glass of "raw" milk nourish or poison you? Pasteurization almost always provides protection from contamination. Unpasteurized "raw" milk, on the other hand, provides a potential breeding ground for disease-causing bacteria such as E. coli, Listeria, Campylobacter and Salmonella, all of which have caused outbreaks spread by raw milk in the past year, said Ynte Schukken, professor of epidemiology and herd health at Cornell's College of Veterinary Medicine.

He has co-authored a paper in the August issue of the Journal of Food Production quantifying the risk of contracting Listeria monocytogenes from raw milk. In collaboration with the U.S. Department of Agriculture's Agriculture Research Service and the New York State Department of Agriculture and Markets, the four-year project of graduate student Alejandra Latorre produced a comprehensive map showing which populations were most at risk when buying from various sources.

"Listeria is one of the most virulent and deadly foodborne pathogens," said Schukken. "Our study demonstrates the relative risk various populations face when ingesting raw milk, including farmworkers, pregnant women, young babies and the elderly. Compared to intermediate-aged adults, these last three groups were particularly susceptible."

The researchers analyzed risk across various purchasing methods including buying from a farm's on-site store, directly from its bulk tank or from a third-party retailer. "Raw milk from retailers proved most dangerous by far. But when it comes to milk, the safest purchasing decision you can make is to buy it pasteurized," Schukken said.

Despite its dangers, 28 states permit the sale of raw milk. Enthusiasts claim health benefits from nutritious compounds supposedly destroyed by pasteurization.

"These claims are not backed by scientific evidence, and several studies have shown them to be myths," said Schukken. "Pasteurization helped revolutionize health, effectively ending diseases such as tuberculosis and Q fever. Bypassing this safety measure could have serious consequences for public health, dramatically increasing bacterial infection and outbreaks."

Other tips to minimize risk, says Schukken: "Make sure the farm is a legal raw milk farm participating in a testing program. Only buy what you can finish in a week, keep it cold in your fridge, and use it quickly."

Carly Hodes is a writer at the College of Veterinary Medicine.