Our “Microbiological tests” package is the modern, standardized and improved version of the “yogurt test” in which starter culture and milk are mixed and the presence or absence of acidification indicate whether the milk is acceptable or not.
In the modern test, milk is added to an agar plug in a tube containing spores of a bacterium and is then incubated at 65°C. The development of a yellow color indicates that the milk is free of inhibitory substances (such as antibiotics), while no change from the initial blue color indicates that the milk is contaminated. The tests need 2 to 3 hours to reach a conclusive result.
Microbiological tests are the tests of choice where a broad range of antibiotics need to be detected—typically in milk control laboratories, but the tests are also suitable for testing of tank samples at farms or milk silos at dairies.