A process for selectively controlling the crystallisation of thermodynamically stable Form or kinetically stable Form polymorphs of mesotrione from an aqueous mesotrione solution, said method comprising adjusting the pH of the mesotrione solutions to a value wherein said thermodynamically stable Form or kinetically stable Form mesotrione is ultimately obtained is disclosed. The piece of equipment is in communication with a network, the piece of equipment having one or more machine-resolvable codes associated therewith. The impeller controls a flow rate of air adjacent to the adjacent to the thermal energy source.