The invention relates to a method for obtaining a valuable product, particularly starch and/or protein, from grain flour, wherein i. the grain flour is mixed into a dough using fresh or process water,ii. the dough is divided into at least two fractions, particularly centrifugally into a heavy A starch fraction, a protein and B starch fraction (nozzle phase of the decanter), and a pentosan fraction, iii. the fractions obtained are used to produce biogas, which is used to generate energy, and iv. wherein the fraction used for the production of the biogas is subjected to at least one liquefaction step (step 505) and a phase separation (step 506), with the biogas being produced from the liquid phase of the phase separation.