A cleaning simulator was used to determine the changes in soil and bacterial numbers on stainless steel surfaces over 30 12-h soiling and washing cycles with four cleaning systems. The soiling milk was inoculated with 5 × 105 Streptococcus faecalis and 5 × 105 Enterobacter aerogenes organisms/ml. One system included a pre-milk rinse of water (20 C), soiling milk (30 C), wash with alkaline detergent (50 C) and two rinses with water (20 C). In the second system, an iodophor sanitizer (25 mg available iodine/L, 20 C) was substituted for the pre-milk water rinse, and in the third the iodophor was substituted for the final water rinse. In the fourth system, the iodophor was applied instead of the final water rinse, but was left for the 9.5-h intercycle period and drained immediately before the next milk soiling. Results showed that the sanitizer can be an important and, under some conditions, the most effective system component in controlling the bacterial population on surfaces. Of the short contact-time sanitizer applications, the post-wash sanitizer was more effective in reducing the bacterial count than the pre-milk sanitizer, but application of the sanitizer for the complete intercycle period completely eliminated all viable bacteria and was thus far more effective than either of the short contact-time methods. It was also shown that the sanitizer can play an important role in the detergency of the system. The organisms studied (S. faecalis and E. aerogenes) differed in their soiling characteristics and survival in intercycle conditions.
1Present address: Dairy Research Centre, P.O. Box 217, Richmond, N.S.W. 2753, Australia.