explained above the improved method is resorted to for increasing the specific volume i e for expansion of tobacco ribs which are already segregated from tobacco leaf laminae the ribs preferably form a continuous stream which is conveyed through a conditioning zone to be contacted by steam so that the steam contacts all sides of the ribs the steam condenses on the surfaces of the ribs and the thus released heat penetrates into the ribs to evaporate the moisture in the inner strata of ribs such expansion entails automatic increase of specific volume puffing of the ribs each increment of the stream is maintained in contact with steam for an interval of time which suffices to insure adequate puffing of ribs the temperature of steam need not be high in fact gradual heating is preferred because this insures intensive wetting of ribs with condensate penetration of condensate into the inner strata of the ribs and gradual expansion of ribs as a result of evaporation of moisture in their interior gradual expansion insures that the specific volume of ribs increases without bursting and attendant noise and comminution i e the ribs are treated gently without fragmentizing apparatus for the practice of the improved method resemble or can resemble that which is described in the commonly owned german offenlegungsschrift no 1 911 103 or 2 402 438 these publications disclose apparatus for thorough wetting of tobacco ribs but without expansion as a result of evaporation of moisture it has been found that the energy requirements of apparatus for the practice of the improved method are not higher than the energy requirements of apparatus which are used solely to increase the moisture content of ribs or to increase the volume of ribs without expansion which is attributable.