Sterile air filters are needed for dairy technology and also for other sterile processes such as in the pharmaceutical industry. They serve, for example, to bleed piping systems after steam sterilisation, to ventilate containers and tanks when the filling levels vary or to decontaminate laminar flow of air in order to hinder that system components which are to be kept sterile come into contact with the contaminated atmosphere. Generally speaking, sterile air filters serve as an interface between a sterile area and the surrounding atmosphere. Therefore they must be viewed as an especially important part of a sterile system and their function significantly influences the quality of the product. The weaknesses of the sterile air filters are often insufficient monitoring, contaminated condensate and, above all, a working life which is too low.