Accuracy, precision and response time of consumer bimetal and digital thermometers for cooked ground beef patties and chicken breasts

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

Submitted to: Journal of Muscle Foods
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/14/2007
Publication Date: 4/2/2009
Citation: Liu, M., Vinyard, B.T., Callahan, J.A., Solomon, M.B. 2009. Accuracy, precision and response time of consumer bimetal and digital thermometers for cooked ground beef patties and chicken breasts. Journal of Muscle Foods. 20(2):136-159.

Interpretive Summary: Consumers have been advised to use thermometers during cooking to ensure that ground beef and chicken products have been cooked to a safe internal temperature to prevent illness. A large study evaluating consumer instant-read thermometers, bimetals, digitals, forks, remotes, digital probe and disposable color change indicator thermometers was conducted in meat products. In this paper, consumer instant-read bimetal and digital thermometers were evaluated for accuracy, response time and reliability in 80 percent and 90 percent lean ground beef patties cooked to 71° C on gas grills and electric griddles, and for boneless and bone-in split chicken breasts cooked to 77° C on gas grills and baked in consumer ovens. After the meat product reached the target endpoint temperature, the product was removed from the heating source and the thermometer was inserted into the cooked meat as close as possible to the thermocouple. Temperature readings were taken at the manufacturer recommended time and also at an extended time (30 s). Bimetal and digital thermometers measured the product temperature as lower than the thermocouple at both the manufacturer recommended time and at an extended time. Based on the results from this study, when consumers use instant-read thermometers to measure product temperature, the products would be safely cooked to a higher temperature and this most likely would negatively affect the quality of the meat product.

Technical Abstract: Three models each of consumer instant-read bimetal and digital thermometers were tested for accuracy, precision and response time compared to a calibrated thermocouple in cooked 80 percent and 90 percent lean ground beef patties and boneless and bone-in split chicken breasts. At the recommended insertion times, the percent of measurements matching a calibrated thermocouple were 14–69 percent for bimetal, and 0–64 percent for digital thermometers. Bimetals averaged 2-11 deg F and the digitals 1-20 deg F less than the thermocouple readings. With longer insertion times, bimetals registered 25–81 percent and digitals registered 14–92 percent of the products as cooked. Bimetals averaged 1-9 deg F less than the thermocouples and the digitals 2-7 deg F less. Measurement repeatability (precision) was high within and between individual thermometers of the same model. Results indicate that the consumer thermometers evaluated in this study required more than the recommended time to register products as cooked.