NC A&T Food Scientist Advises on Meat Thermometers

July 9, 1997

Greensboro, NC: It once was acceptable to cook a hamburger until the juices ran clear and it was no longer pink in the middle. Not anymore, according to the United States Department of Agriculture.

A recent statement issued by USDA cites research that shows even brown burgers may not have reached a temperature high enough to kill the dangerous form of E. coli bacteria, O157:H7. Therefore, instead of relying on color, USDA recommends using a meat thermometer to know that the meat has reached 160 degrees Fahrenheit, the temperature at which bacteria die.

"Because they are a ground product with an inside consisting of the same matter as the outside, hamburgers have a higher likelihood of carrying the E. coli bacteria," said Dr. Aubrey Mendonca, a microbial food safety research scientist with the North Carolina A&T State University School of Agriculture. "It is for this reason that hamburgers must be cooked thoroughly, and a meat thermometer is the best way to ensure that this is done."

According to Mendonca, steaks and other cuts of meat packaged as a solid piece can still carry E. coli, but the bacteria is usually on the outside where cooking temperatures kill off bacteria more quickly. With a hamburger patty, or ground beef, on the other hand, E. coli is equally likely to be present, both internally and externally.

"E. coli is transferred to the meat product from the fecal matter of infected cattle," said Mendonca. "Therefore, it remains on the surface unless improper handling introduces it under the surface, or, in the case of hamburger patties, the surface becomes part of the middle."

Though intended to enhance safety, improper use of meat thermometers can give users a false sense of security and even transfer the bacteria.

To prevent such mishaps, Mendonca offers these suggestions:

• Purchase a metal-stemmed thermometer with a numerical scale that is easy to read.
  
• Wash, rinse and sanitize the thermometer completely between each use and before checking other foods.
  
• Insert the thermometer in the thickest part of the food to ensure that the center has reached 160 degrees Fahrenheit.
  
• Calibrate the thermometer if it has been dropped or exposed to extremes in temperature.

Calibration techniques recommended by Mendonca include:

• For measuring high temperatures, insert the thermometer in a pot of boiling water and check to see that it registers 100 degrees Celsius or 212 Fahrenheit. If it doesn't, adjust the calibration to that temperature.
  
• For measuring low temperatures, insert the thermometer in a pot of ice slush and check to see that it registers 0 degrees Celsius or 32 Fahrenheit. If it doesn't, adjust the calibration to that temperature.

According to the Centers for Disease Control and Prevention, E. coli O157:H7 infects 20,000 Americans and kills 200 each year.

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For more information, please contact Dr. Aubrey Mendonca, NC A&T School of Agriculture, (336) 334-7328.