Abstract: The invention relates to method for the stepwise removal of bacteria from a fermentation broth. According to said method, the bacteria in the fermentation broth are mixed with a retention promoter mixture in a first process step and the pretreated bacteria are removed by precoat filtration in a second process step. The inventive method uses a retention promoter mixture from bentonite and polycations such as PEI or polyDADMAC and is suitable for treating large quantities of bacteria. The filter cake obtained with bentonite/PEI has a substantially improved quality.