TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The torrefaction plant comprises a torrefaction storm, and a biomass supply device, which is a feed drum or a screw. The weighing device has a belt scale, a Coriolis mass flow meter, and a differential weigh feeder comprising a screw conveyor for an inert compound with the torrefaction plant. The thermal mass flow meter comprises at least one sensing element, and a device for measuring the heating capacities of the measuring element. The measuring devices are arranged for the density, the mass difference, the gas compositions, the average heat capacity, the mass flow rate, the organic components and/or the gas amount difference.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The auxiliary parameter is calculated by determining the: mass difference of the mass of the biomass before torrefaction and/or the mass of the biomass after torrefaction; and product of the differences of gas compositions and average heat capacities of flue gas before and/or after torrefaction from exhaust gas. The mass difference of the biomass before and/or after torrefaction is calculated by a respective weighing device at an inlet and an outlet of the biomass in or from the torrefaction plant. The product is determined using a thermal mass flow meter and a temperature at the inlet and/or the outlet of the biomass. The auxiliary parameter is determined by: measuring a density difference of the density of the biomass before and/or the density of the biomass after torrefaction; organic components of the flue gas before and/or organic components of the exhaust gas after the torrefaction; and a gas volume difference of the flue gas at the inlet before and the exhaust gas at the outlet after torrefaction. The density of the biomass is radiometrically determined. The organic components are determined using IR-sensors or by gas chromatography. The amount of gas difference is determined using dynamic pressure, gas velocity or Coriolis effects. The step of controlling the torrefaction plant is carried out for a residence time of the biomass in the torrefaction plant and/or at a temperature of the flue gas.