sealPurdue News

May 2000

Most foodborne illnesses stem from improper cooling

WEST LAFAYETTE, Ind. – Nationally reported incidents of foodborne illness caused by E. coli bacteria have increased consumers' awareness of the importance of proper food handling and thorough cooking, but the most common cause of food-related sickness is far from common knowledge.

"Improper cooling is the No. 1 reported cause of foodborne illness in the United States," says Richard Linton, an associate professor of food safety at Purdue University. "Most people recognize the need to cook foods to a temperature above 140 degrees in order to destroy most microorganisms that might be present, but they don't realize that any leftovers have to be cooled quickly so as not to allow any surviving bacteria to grow."

The U.S. Food and Drug Administration recommends that cooked food be cooled to the refrigeration temperature of 41 degrees Fahrenheit in less than four hours, but Linton says that's not as easy to accomplish as it sounds. He demonstrates this for his classes by preparing a big pot of chili and then measuring the amount of time it takes to cool to the recommended temperature.

"I cook the chili at 165 degrees and then let it cool to 140 degrees before placing the pot in a refrigerator that's set at 37 or 38 degrees," Linton says. "I then ask them how long they think it will take to cool down to 40 degrees. Rarely do I get a correct answer, which is between 20 and 24 hours."

Even people who have been cooking a long time may not realize the potential hazards of not cooling foods properly.

"How many people allow their Thanksgiving turkey to cool at room temperature for a couple hours before placing it in the fridge?" Linton asks. "If you've cooked it to the right temperature, you've killed all the bugs that are going to cause a problem right then. But bacteria thrives in that window between 140 and 40 degrees, and even a turkey carcass that's refrigerated immediately after it's carved is going to be in that temperature range a lot longer than four hours."

Consumers can speed up cooling time by using stainless steel containers that facilitate heat transfer; dividing food into smaller, shallower containers; slicing meat off the bone; stirring the food as it cools; or placing the container of food in an ice-water bath before putting it in the refrigerator.

CONTACT: Linton, (765) 494-6481,

* To the Purdue News and Photos Page