TEMPERATURE AND MICROBIAL FLORA OF REFRIGERATED GROUND BEEF GRAVY SUBJECTED TO HOLDING AND HEATING AS MIGHT OCCUR IN A SCHOOL FOODSERVICE OPERATION1

Abstract

The practices of handling precooked chilled gravy in school kitchens were simulated to determine if they could contribute to outbreaks of foodborne illness. Time-temperature measurements and bacteriological tests were made at intervals during chilling, holding, and heating of gravy. Sixty-six pounds of cooked ground beef gravy were packed hot (158 F, 70 C) in bags, cooled in chilled water for 1 h, and refrigerated for 16 h. The gravy was held for 5 h at 82 F (28 C) and at 42 F (5.5 C) and then it was heated in a compartment steamer for 35 min. After 1 h cooling in chilled water, the mean temperature of gravy was 82 F (28 C) and after 16 h of refrigerated storage, the temperature was 45.5 F (7.5 C). The mean temperature of chilled gravy held at 82 F (28 C) remained about 50 F (10 C) for 4 h and reached 64 F (18 C) at the end of the 5-h holding period. The mean temperature of gravy held under refrigeration for 5 h decreased 2 F, from 45.5 F (7.5 C) to 43.5 F (6.5 C). After 35 min of heating in a compartment steamer, the highest temperature was 136 F (58 C) for gravy initially at 65 F (18.5 C) and 128 F (53.5 C) for gravy initially at 47 F (8.5 C). Bacteriological tests indicated that the greatest increase in the number of total aerobic bacteria in gravy occurred during cooling rather than holding. Although some samples yielded coagulase-positive staphylococci, the numbers changed little during holding or heating. Clostridium perfringens was not found in any samples of the gravy.