When we first started selling the Fresh Roast SR 300 and SR 500, we recommended a certain technique for an even roast; namely, to remove the chaff collector and stir the coffee during the initial stages of the roast when the beans are heaviest. It turns out that this results in an inordinate amount of chaff getting sucked back into the base of the roaster (because the fan is drawing in air to cool the roaster) and over time it chokes the unit. Eventually the unit will no longer get hot and the chaff in the base presents a fire hazard.