Abstract: Method and apparatus intended for the filtration on a membrane of a product such as milk with a view to analysing filtration products recovered on the membrane. The method comprises the filtration under pressure and the rinsing by means of different elements without any risk of deteriorating or polluting the active filter. The apparatus which comprises two active elements (100) and (200) is particularly characterized by the combination of means for supplying a pressurized tank (3) with different liquids, and a filter holder (10) which is wedged by means of two inclined planes (P1) and (P2) driven by means of a jack (14) so that they are sealingly superposed. The invention applies particularly to the analysis of milk with a view to numbering the Clostridium Tyrobutyricum, or any other microorganism.