The method consists in preparing of poured plates using a specified selective culture medium and a specified quantity of a test sample, further dilutions of the test sample. Then aerobic incubation of the plates at 25 degrees centigrade for 3, 4 or 5 days, followed by calculation of the number of yeasts and moulds per gram or per millilitre of the sample from the number of colonies obtained on plates chosen at dilution levels so as to give a significant result.