The present invention relates to a process for fermenting Bordetella comprising a) providing a sample of bacteria of a Bordetella species； b) incubating the sample of bacteria of a Bordetella species in a first environment under at least one bvg (Bordetella virulence genes) modulating condition for at least 5 generations, thereby producing a mature culture； c) incubating the mature culture in a second environment in the absence of the at least one bvg modulating condition； wherein step c) occurs after step b).
