The invention relates to a novel method for producing mononatrium trihydrogen pyrophosphate and to the use of products produced by said method as acidifiers, buffering agents and complexing agents. The novel method is characterised in that glassy, acidic natrium polyphosphate containing a Na/P ratio of 1: 2 in fine powder form is tempered at temperatures ranging between 100 and 200 DEG C in moist air with a steam pressure of between 10 and 200 mBar, or in a polar solvent, in which the phosphate is insoluble, in the presence of a quantity of water sufficient for the hydrolysis, until the mass has been predominantly converted into NaH3P2O7.