Phew, I certainly appreciate the way you are managing your roasts, though I don't have a clue how you managed the mechanics, bean chemistry, or the heat physics involved. It is a 'leap of faith' for me. I call your system with the Gene the Kierkegaard Method.
Sorry - I wasn't trying to be mystical or unclear, but given the known vagueness of the Gene Café's temperature sensors I think that trying to be 'precise' is misleading, or at least somewhat optimistic.
What I think is important is that, given the Gene's somewhat underpowered heating element, the best way I've found to achieve reasonably repeatable roasting profiles is to attack the problem by aggressively managing the airflow through the roaster - something which a large shop vacuum on a Variac does quite well.
Just to clear up any confusion, I'm using the large GC chaff collector:
A 3" dryer hose feeds from the collector's top vent to a shop vac on the floor, and the vac exhausts through a 2 1/2" hose run outside under the garage door.
While this lash up is very good for controlling the airflow through the roaster, it still doesn't address the underlying issue that the GC's heating element is somewhat marginal, especially for large beans like Monsooned Malabar or Mysore Nuggets which tend to get baked, not roasted.
I'm currently experimenting with a technique that some very large automated commercial roasters use - which is to pre-heat the incoming air in a plenum chamber before it enters the roaster. Since the GC draws its fresh air from a vent in the lower right front corner, it's a simple matter to construct a wooden plenum chamber 15" wide, 5" deep, and 4" high with an open top on which the Gene Café sits - a 1 1/2" hole on one edge of the chamber neatly fits my original roasting heat gun, which provides enough calories to raise the air temperature inside the plenum to 150-170 degrees in under a minute.
I'm still developing and refining this new process, but essentially I preheat the plenum to about 150 degrees, begin the roast, and continue to preheat until the beans mass begins to change color (3-4 minutes, roughly 375-400 degrees ), cut off the preheat, and allow the GC to control the roast until just after ST crack. At which point I turn preheat back on and use the shop vac to control the temperature until I reach the desired roast level.
A word of caution - if you want to try this for yourself, be aware that the GC's fan does NOT appear to be molded from high-temperature plastic, so I'm being VERY careful not to allow the plenum temps to exceed 200 degrees.
Cheers
Jim
