This processing option is the eldest known industrial pelletizing technique. First all ingredients are blended, then by adding liquid a wet dough is formed, which is passed through an extruder with defined dye sizes. If a thick-wall extruder (approx. 4 mm) is used and the ratio liquid/solids is well adjusted the extrudates break up into 1mm particles during the beginning of spheronization, warranting a high yield of homogenously sized pellets. However, minimum particle size is limited to about 500 µ. Despite a high reproducibility this is a somewhat tedious process as it involves many process steps, i.e. dry blending, wet massing, extrusion, spheronization, drying and involves different equipment with a large total product contacting surface. The uniform particle size allow for an equally uniform subsequent functional coating. In many pharmaceutical applications the uniform particle size is often only achieved if the formulation includes 20-50 % of microcrystalline cellulose.
In the pharmaceutical industries the particle size usually ranges in between 500 and 2000µ, in the food and feed industries size can however rise to several centimeters.