The conventional way of detecting becteria is incubation.In this,samples of beer are filtered through a membrane and the residue collected is placed on agar plates. After incubation, any bacteria colonies that form are separated out and cultivated again until pure strains are produced that can be identified under a microscope. It works, but it's very time consuming because the incubation takes two to five days, so by the time the bacteria is detected, it may be too late to save the affected batch.