The damper... not unleavened bread...
I wanted to introduce you to the damper... one of the key controls on a coffee roasting machine.
But first a quick reminder about the convection heating loop which drives much of the roasting process. Environmental air enters the roaster from below the burners, is heated by those burners (which also directly heat the drum) and then the heated air moves through the drum (roasting the coffee beans on its way) and then through to the exhaust. That hot air movement is partly caused by the flue being above the roaster drum (hot air rises), but mostly through a pressure difference created by an exhaust fan.
The damper allows the coffee roaster to change the amount of resistance to air flow that goes through the exhaust. The damper lever moves a piece of metal in the shape of a semicircle which progressively blocks the outlet. The outlet resistance affects two things: heat loss/gain in the roasting chamber, and velocity of air passing through the drum. The more open the damper the faster air passes through the drum (potentially increasing the rate of convective roasting) and the more heat leaves the chamber (potentially lowering the rate of convective roasting). The opposite happens when the damper is more tightly closed. There's a balancing act between heat retention and air velocity when it comes to their combined heating effect on the coffee beans themselves which is also dependent on the size of the roasting load.
Use of the damper is a single factor solution to a multifactorial problem!
To read about burr geometry click here
To read more about coffee burrs click here