A method for micronization of a dispersion of particles comprising a proteinhaving a predetermined level of biologicalactivity. The method comprises introducing the dispersion into a vortexchamber milling apparatus under milling conditionswhich result in a protein powder having a particle size distribution of 5 to100 µm and/or exhibiting a 30 to 400 fold size reductionof the protein particle dispersion from its original size, and retaining atleast 80% of the predetermined level of biological activityof the protein. The milling conditions include one or more parameters selectedfrom the following: input pressure between 1 and 7Bars； injector pressure between 0.2 and 5 Bars； loading rate between 0.1 and 5kg/hour； and gas flow between 30 and 100 m3/hour.
