Comparing Infrared and Probe Thermometers to Measure the Hot Holding Temperature of Food in a Retail Setting

In Ontario, potentially hazardous food that is kept hot must be held at an internal temperature of ≥ 60°C. This limits the use of infrared thermometers for food safety compliance, as they show only the surface temperature of foods. This research examined the relationship between the internal temperature of hot-held foods measured via a probe thermometer and the surface temperature measured via an infrared thermometer in a retail setting. Seven different food items in hot holding stations at seven different retail stores were examined on six occasions for probe and infrared temperatures. The data were analyzed descriptively, and a multivariable linear mixed-effects model (controlling for store location as a random effect) was developed to determine the predictive relationship of infrared to probe thermometer measurements. A strong correlation was identified between the two measurements (r = 0.706; n = 212). The regression model indicated that the infrared temperature significantly predicted the probe temperature, and this relationship differed by food type. The minimum infrared thermometer temperature needed to predict a probe temperature of ≥ 60°C, with 95% confidence, ranged from 53°C for whole chicken to 62°C for chicken strips. These results can be used to inform temperature compliance monitoring for hot-held foods.