The method is applicable to cereals and cereal products as well as to certain products containing less the 1 % of crude fibre. It consists in boiling with a mixture of acetic acid, nitric acid and trichloroacetic acid (after any necessary grinding and defatting). Then separation and washing of the insoluble residue on a filter crucible. Drying and weighing of the insoluble residue, and determination of the loss of mass on incineration.