Permanent Pipe Lines for Dairy Plants

Abstract

Summary A permanent sanitary pipe line consisting of four polishes of stainless steel and pyrex glass was installed at the University Dairy. Study was made to determine if such a line could be satisfactorily cleaned by rapid circulation of acid and alkaline detergents and sanitized by the circulation of 180° F. water. Milk samples were taken from the inlet and outlet of the pipe line and examined for mesophils, psychrophils and coliform organisms. Measurements were also made of the pH of the milk. Similar samples were stored at 40° F. for 7 days and again examined as before. Sections of the tubing were swabbed regularly to determine the presence of mesophils remaining on the surface of the pipe line after sanitization. Visual inspection of the line was made weekly. Comparison of sections which had been in service was made with a control consisting of a brush-washed section of stainless steel. A further test was made by vigorously rubbing a clean, white flannel within the pipe to pick up any loose deposits. There was no measurable pick-up of organisms resulting from the use of the permanent pipe line. Samples of milk that had passed through the pipe line were held at 40° F. for 7 days. These samples showed no marked growth of mesophils and only slight increases in psychrophils. Only slight changes in pH occurred during the storage period. There were nearly as many changes to a higher pH as to a lower pH. Swab counts on the pipe line were low. While sterility was not attained the results would be judged excellent by the standards recommended for restaurant utensils. Bacteriologically speaking there was no choice between the four polishes of stainless steel and the pyrex glass. Under the conditions of this study, a permanently installed pipe line of either stainless steel or glass was found to be satisfactory from a sanitary point of view.