Abstract: A method of controlling the spray droplet size of a spray nozzle apparatus, in particular for the manufacturing of food powders, delivered to the spray nozzle comprises the following steps: a) providing a paste of a product to be sprayed by a spray nozzle; b) continuously determining the shear viscosity (?) of the product paste delivered to the spray nozzle; c) determining the mass flow rate (Qm) of the product paste delivered to the spray nozzle; d) determining the static pressure (P) of the product paste delivered to the spray nozzle; e) determining the density (p) of the product paste delivered to the spray nozzle; f) delivering the data obtained in steps b) to e) to a control device comprising a computer and a memory; g) calculating control data for adjusting the spray nozzle on the basis of the data obtained in steps b) to e) and on nozzle geometry parameters stored in the memory; h) sending the control data as control signals to a control means of the spray nozzle and adjusting the spray nozzle accordin