Exploring Temperature Patterns of Leafy Greens in Institutional Kitchens

Introduction:  Leafy greens have been linked to over 40 outbreaks of foodborne illness since 1990. As potential pathogens such as Escherichia coli O157:H7 can grow on or in cut leafy greens at temperatures above 5°C, the U.S. Food and Drug Administration recommends that leafy greens be kept at refrigerated temperatures (5°C or lower).

Purpose:  There is a lack of research in determining the temperature profile of leafy greens within a food service establishment, especially the variation in temperatures through storage, preparation, serving, restorage, and reservice. The purpose of this study was to determine the temperature profiles and patterns that leafy greens in single serving clamshell containers were exposed to through a typical school meal program.

Methods:  Temperatures of ready-to-eat leafy greens (whole head and cut/shredded) were recorded using data loggers, infrared and probe thermocouples in 20 schools over a 3-day period. Temperatures were taken by stabbing the probe into the leafy green, or through a thermocouple in the case of the data loggers; temperatures were taken in storage coolers, on the line, and in the prep cooler.

Results:  Data showed that temperatures of leafy greens in clamshell containers reached above 5°C for more than 3 hours throughout the process as high as 8°C. Various temperature patterns were seen, including temperatures rising above 5°C for at least one hour up to 3 consecutive days. Leafy greens were shown in all cases to be exposed to temperature variability. 

Significance:  The results show the importance of developing a standard for thermometer use and temperature monitoring of leafy greens in school kitchens to avoid the potential for harmful pathogen growth. This data can be used both in risk assessment calculations and as an example to show food handlers the importance of a strict temperature verification regime.