Batch and fed batch cultivations of Xanthomonas campestris with varying amounts of the N source (NH4Cl) yield xanthan polymers which differ in pyruvate content. Analyzing the rheological properties of the xanthans produced exhibits that it is not only the molecular mass but also the pyruvate content that affects the viscosity of xanthan solutions. However, there is obviously no simple functional dependency but rather a step increase in viscosity when going from below 2 to above 3 wt % of pyruvate.