Identification and control of processing variables that affect the qualityand safety of fluid milk

The objective of this study was to increase quality and safety of fluid mil k by eliminating postpasteurization contamination as measured by extended s helf life. Milk shelf life was defined as the number of days for standard p late count to reach 20,000 CFU/ml in milk stored at 7 degrees C. Sequential analysis of the fluid milk processing system indicated filling machine and pasteurizer were significant sources of postpasteurization contamination. Aseptically sampled milk from the pasteurizer outlet indicated a maximum sh elf life of more than 30 days could be achieved. The pasteurizer can be a s ource of contamination when inadequately cleaned or maintained. The filling machine was a significant source of contamination. Shelf life of milk in 2 36-ml containers was reduced 20 days compared with milk sampled before the filling machine. Carton-forming mandrels, filling heads, and airborne micro organisms were sources of contamination within the filling machine. Elimina ting sources of postpasteurization contamination and proper cleaning follow ed by sanitizing with chlorine significantly increased milk shelf life in p aperboard containers; to 20.4 days from an initial shelf life of 9 days. Ch anging the sanitizing agent to peroxyacetic acid significantly increased mi lk shelf life to 33.9 days, Enclosing the filling chamber and adding steril e laminar flowing air significantly improved microbiological quality of air inside the chamber and reduced variance among milk shelf life samples.