Abstract: A method and an apparatus for removing impurities from plant fibrous material which constitutes residual products in the refining of tuber or root vegetables, fruits etc. The plant fibrous material is, for forming a first substance, adjusted to a TS content of at least approx. 25% whereafter the first substance is fractionated in a first screening device to form a first fraction. The TS content of the first fraction is reduced, for the formation of a first mass, whereafter the mass is dried, for the formation of a second substance. This is fractionated in a second screening device to form a second fraction which substantially exclusively consists of plant fibres.