Accuracy of consumer bimetal and digital thermometers in cooked ground beef patties and chicken breasts

Authors: Liu, Martha; Vinyard, Bryan; BOARMAN, JANICE; Solomon, Morse

Submitted to: USDA Annual Food Safety Research Planning Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 2/20/2007
Publication Date: 2/21/2007
Citation: Liu, M., Vinyard, B.T., Callahan, J.A., Solomon, M.B. 2007. Accuracy of consumer bimetal and digital thermometers in cooked ground beef patties and chicken breasts [abstract]. USDA Annual Food Safety Research Planning Meeting.

Interpretive Summary:

Technical Abstract: The only way to determine if meat products have been cooked to an internal temperature necessary to inactivate pathogens is to use a thermometer. To date, the accuracy and reliability of consumer instant-read thermometers have only been evaluated in water-baths, not in meat products. Ten units of three different commercially available consumer instant-read bimetal (B1, B2, B3) and three digital thermometers (D1, D2, D3) were tested for accuracy compared to a calibrated thermocouple (TC) in preformed 80 percent and 90 percent lean ground beef patties cooked to 160 deg F on gas grills and electric griddles, and boneless and bone-in chicken breasts cooked to 170 deg F on gas grills and baked in consumer ovens (n=36 for each meat product and cooking method). Once products reached the target endpoint temperature using the TC, the product was removed from the heat source and the test thermometer was inserted into the product parallel and as close as possible to the TC. Times and temperatures of the test thermometer and TC were recorded at two predetermined times: manufacturer or FSIS recommended time (RT; 20 s for bimetal and 10 s for digital thermometers) and at a predetermined endpoint time (EP; 30 s) or recorded if the thermometer reached the target temperature before the RT or EP. The test was discontinued when the thermometer reached the target endpoint temperature or EP. At the RT, the percentage of beef and chicken samples registered as cooked was 25-69 percent for B1, 14-50 percent for B2, 17-47 percent for B3, 0-28 percent for D1, 11-64 percent for D2, and 0-22 percent for D3. All test thermometers averaged temperatures less than the TC at the RT; the temperature range was 2 to 10 deg F less than the TC for B1, 3 to 11 deg F less than the TC for B2, 4 to 11 deg F less than the TC for B3, 12.3 to 19.8 deg F less than the TC for D1, 1 to 13 deg F less than the TC for D2, and 11.3 to 15.9 deg F less than the TC for D3. Increasing the time to the EP resulted in an increase in the percentage that the thermometer registered the beef and chicken samples as cooked; 42-81 percent for B1, 33-67 percent for B2, 25-64 percent for B3, 19-64 percent for D1, 25-92 percent for D2, and 14-64 percent for D3. These results indicate that consumers using these bimetal and digital thermometers would cook ground beef patties and chicken breasts to higher temperatures than necessary to destroy harmful microorganisms. Although cooking to these temperatures would ensure a microbiologically safe product, it would negatively affect the quality of the products.