A study was made showing relationship between post-pasteurization contamination of milk and cream and increase in bacterial count of bottled and paper carton products during storage at 45 F for 5 days. A survey indicated extensive post-pasteurization contamination in plants not employing this type of keeping quality test. The 5-day at 45 F test was more sensitive than the coliform test in detecting post pasteurization contamination. Excessive numbers of thermoduric bacteria in the raw supply also were detected by this method when plant equipment was properly cleaned and sanitized.

Special in-line sampling techniques were developed to determine source of contamination. One procedure employed sterile disposable hypodermic syringes inserted through rubber stoppered nipples welded into lines at different locations in the system. Another technique involved removal of samples by insertion of sterile disposable hypodermic syringes through rubber or neoprene gaskets between joints in different locations in the plant.

Bottle and paper carton filler equipment offered special cleaning and sanitizing problems and suggestions were made on steps to minimize contamination from these sources.

Application of the 5-day at 45 F keeping quality test followed by careful study of contamination sources has greatly improved shelf life of pasteurized fluid milk and cream and has represented a real economic advantage to plants adopting the program.

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Author notes

1Technical Paper No. 1773. Oregon Agricultural Experiment Station. Contribution of the Department of Microbiology.

2 Presented at the 50th Annual Meeting of the International Association of Milk and Food Sanitarians, Inc., October 22-25, 1963, at Toronto, Canada.