The invention concerns a method whereby: (E1) an inner liquid phase is made to flow in an inner flow member, and an outer liquid phase in an outer flow member, the flow of the inner liquid phase opening within the flow of the second liquid phase; and the temperature and pressure in the contact area between the first and second liquid phases being such that the first and/or second liquid phase is in the supercritical state, (E2) the flow rate of the inner phase and/or outer phase is varied in such a way as to modify the flow profile, and a torque is identified from values of the flow rates of the inner and outer phases, called transition flow rates, from which the modification in the flow profile occurs (from drops to a jet; or from a jet to drops); (E3) from the transition torque identified in step (E2), the value of the interfacial tension between the two inner and outer liquid phases is calculated, or the result obtained is compared to that obtained for another torque in the conditions of steps (E1) and (E2).