Evaluation of the Microbial Quality of Raw Milk1

Abstract

Commercial evaluation of the microbial quality of raw milk presents a major challenge, and new methods are burdened by being compared to imprecise presently used standard methods. Extensive comparisons in commercial and research laboratory environments were made using a method that involved direct enumeration of single cells in comparison to colony forming units. The correlations were from 0.50 to 0.99 depending on treatment of the data. Repetition of all tests on milk from individual farms indicated that inherent variation in quality at the farm, sampling, testing, and evaluating the results showed the extreme inadequacy of the presently established methods of grading raw milk. More frequent tests with appropriate averaging would improve the likelihood of correct decisions on quality grade.