The invention relates to a method for producing a binder composition, without using a compound selected from the class of phenols. The method comprises: (i) heating an aqueous composition comprising lignin in the presence of a catalyst; (ii) mixing a crosslinking agent with the aqueous composition from (i) and heating the same at a temperature of 60-95° C. for pre-polymerizing lignin and crosslinking agent; (iii) mixing tannin with the aqueous composition from (ii) for polymerizing tannin with the pre-polymerized lignin and crosslinking agent until a binder composition with a predetermined viscosity value is formed; wherein the molar ratio of crosslinking agent to lignin and tannin is 0.5-1.7.