Considerable progress has been made in recent years with the optimisation of grain refinement practice. In the past this could only be done by trial and error which is time consuming and far from ideal. More recently it has been possible to study and quantify the various factors affecting grain refinement including melt nucleation level, growth restriction, grain refiner recovery, in line treatments and potency and variation in grain refiners with the help of the Opticast technology which allows data to be generated from sampling the melt in real time. It has been found that whilst it is useful and necessary to quantify the foregoing furnace factors it is equally necessary to control grain refiner variation in order to achieve a fully optimsed result and to support this, a new grain refiner, Optifme, has been developed and introduced in a number casthouses. The results from two casthouses where these techniques have been applied are reviewed.