A direct-fired steam generator used for supplying steam for re-hydrating dry crop during baling is controlled so as to produce a desired constant steam temperature output by collecting data from which the heat output of the steam generator can be calculated and using this calculation together with the difference between the actual steam temperature and the desired steam temperature to control the amount of process water sent to the steam generator in order to correct any error in steam temperature. Steam temperature is measured in either one of the steam injection manifolds or in an injection tube coupled to an injection manifold so as to be close to the point of application of the steam to the crop.