A grinding mill grinds grains or similar foodstuffs, while the concept of the invention could also be applied to other feed materials. The grain is fed at a controlled rate to an impeller chamber, ground by the impeller until a small enough size to fit through a sieve, and separated into a sample cyclone stream and a bulk or waste cyclone stream. Each cyclone includes a central air return duct which channels air back to the grain feeder chamber and then into the impeller chamber. By having the air from grinding recirculated back to the grinder after separation, the grain grinding process is cleaner and results in less moisture loss.