The method is applicable to products having oxidizing or reducing matter contents equal to or greater than 0.001 % (m/m). The principle is based on detection of the presence of these matter by a preliminary qualitative test. In the case of oxidizing matter adding of potassium iodide solution and titration of the liberated iodine with sodium thiosulphate standard volumetric solution until the blue colour disappears. In the case of reducing matter transferring of the test portion to an exactly measured volume of iodine solution and titration of the excess of iodine with the sodium thiosulphate standard volumetric solution. - Cancels and replaces ISO Recommendation R 908-1968.