Experiments for the counting of yeasts and molds in fresh cheese and raw milk.

As the substrate yeast extract-glucose-chloramphenicol agar (YGC agar) also furthers the growth of other bacteria strains as e.g., Pseudomonas fluores cens, it does not have sufficient selective properties for determining the counts of yeasts and molds in milk products. Therefore, it is recommended t o generally proceed to an acidification of the substrate YGC agar with tart aric acid to a pH of 4.6. All the more, as this does not have a negative im pact on the fungal count. Both the spread-plate and the pour-plate method a re well suited for the quantitative determination of yeasts and molds, alth ough it had been stated in the past that slightly lower fungal counts were obtained under certain prerequisites at using the pour-plate method. This w as due to the the fact that after the mixing of merely 0.1 ml sample or sam ple dilution, heat-sensitive yeasts could be damaged in the still 50 degree s C warm agar substrate. Furthermore, the slightly shorter incubation time of the spread-plate method often represents an advantage. Nevertheless, the shortest incubation time of 4 days stipulated in the common regulations is sufficient for the pour-plate method, too. As incubation temperatures of a pprox. 21 degrees C are required and as the growth of some molds is already limited at 30 degrees C, 25 degrees C as incubation temperature should be observed for other foods, too. The use of 10 g sample being representative for coagulated products as e.g., quarg, can be problematic above all in the case of low yeast concentrations. This is due to individual yeast colonies in fresh cheese which, despite a thorough sample mixing, do not allow a ho mogenous distribution.