I know this has been discussed before, but an ideal solution still seems to be a bit elusive. I've been using a SC/TO setup now for the better part of a year, and trying to find a method to measure temp that is not either bouncing all over the place or just measuring too high. I've been using the k-type digital thermometer that sweetmarias sells (MS6500), and placing the probe through a slot in the 2" wide aluminum collar between the SC and Sunpentown TO. The tip sticks in approximately 2-3" toward the center of the whole assemply and is nearly equidistant between the fan of the TO and the mass of beans tumbling around below (so it's about 2" from the bean mass). I don't roast big batches because I roast everything seperately, using 200 gm batches.
What I found was that my warmup phase (if trying to stick to 300 deg) would take a VERY long time (way more than 3-4 min), but would be reasonable at 350 or even a tad higher. First crack typically ocurred around 470-480, and second near 500. All of that just seemed too high. Recalling several posts here (and maybe on coffeegeek), I remember the debate about monitoring temp in the bean mass vs air inlet temp, and thought that settled on the air inlet measurement. A thread popped up on greencoffeebuyingclub discussing this in some more detail again, so I experimented with bean mass temps. What some people suggest is to bury the probe in the bean mass for 60-80% of the time (since burying it 100% would likely be impossible in my setup, unless I just jb-weld the probe along the bottom of my SC pan), and what I got were (as you'd guess) temps fluctuating by as much as 25-30 deg (it drops when covered by the beans, then quickly rises when exposed to hot air). One thing about this thermo setup- I don't think the probe is well calibrated, because it fluctuates by maybe 1 deg at low temps, and by as much as 5-7 deg at higher temps (especially as I close in on 1st crack around 450 and >).
How the heck do you guys (or gals?) measure temp in a similar set up? My k-type is the floppy variety- would drilling a hole in the sc and placing a rigid probe in there do the trick? Should I just subtract 30 deg from my air inlet temp, assumming the bean mass temp is really that much lower? Bottom line- I can produce good results no matter what the thermometer reads as long as I stick to the rules of 3-4 min warmup getting all beans a similar shade of yellow, sprint to 1st crack and plateau the temp trying to prolong onset of 2nd crack. It would just be nice if my readings jived with everybody elses.. I kinda feel "left out"!
Any ideas are most welcome.
Ray
