Cooling Eggs to Prevent Salmonella

November 18/American Society of Agricultural Engineers -- A Purdue University food scientist believes the poultry industry could implement a rapid egg cooling technology to reduce future outbreaks.

Kevin Keener, an associate professor of food science, said quick cooling of eggs after they are laid would significantly reduce the ability of Salmonella to grow inside eggs and potentially keep consumers from getting sick. There are no federal guidelines for how quickly eggs should be cooled, but current industry procedures can take as long as six days to cool eggs to 7°C (45°F), the temperature at which Salmonella can no longer grow. Keener's rapid-cooling technology would take two to five minutes.

Keener said eggs can be more than 38°C (IQO°F) after washing and packaging in cartons. Some 30 dozen eggs are then packed in a case, and 30 cases are stacked onto pallets and placed in refrigerated coolers. The eggs in the middle of the pallet can take up to 1.42 hours to cool to 7°C (45°F). He said scientists estimate that one in about every 20,000 eggs has Salmonella naturally inside.

"The eggs in the middle of a pallet may take up to six days to cool, and if the one in 20,000 that has Salmonella is in the middle, the bacteria will grow," Keener said. "In reality, some eggs don't cool to 7°C (45°F) until they're in the refrigerator in your home."

Keener said FDA studies show that if eggs were cooled and stored at 70C (45°F) or less within 12 hours of laying, there would be an estimated 78% fewer Salmonella illnesses from eggs in the U.S. each year.

Keener's cooling technology uses carbon dioxide "snow" to rapidly lower the eggs' temperature. Eggs are placed in a cooling chamber, and carbon dioxide gas at about minus 43°C (minus 110°F) is generated. The cold gas is circulated around the eggs and forms a thin layer of ice inside the eggshell. After treatment, the ice layer melts and quickly lowers the egg's internal temperature to below 7°C (45°F).

The eggshell does not crack during this process, because the shell can resist expansion from a thin ice layer.

Previous studies have shown the cooling treatment would increase shelflife by four weeks.

Keener has a prototype of his rapid-cooling technology in his Purdue laboratory and is working to optimize its function.

For more information, contact Kevin Keener,

From the November 29, 2010, Prepared Foods E-dition