I finally got to try a test roast with the dual thermocouples today. Until now, I've been roasting my sound, sight and smell.
At the same time, this was also a test of a new stir arm, plagiarized from Peter's design and a test roast with just 1 cup of Kona beans that I wanted to take to city+. The first time I roasted these beans, I only took them to barely past 1c and they were a bit sour.
I enjoy roasting and hope having both environment temp and bean temp will help me better reproduce results, once I somewhat figure out what the heck I am doing
Ambient temp was 80f and I set the T1 thermocouple low under the spacer ring so it would be in the bean mass, with the T2 over the ring so it would read ET about mid point from the SC plate and the top of the TO glass.
Started with 1 cup of green beans @ 175gm -- roasted weight was 145gm and about 1 3/4 cups -- the just roasted beans smell slightly sweet (brown sugar?) in a glass jar.
Preheated the TO to 300 and when ET thermocouple said 300, dropped beans in and turned TO to 350
At ~4minutes beans were just starting to turn tan, turned TO to 400
@ ~8 minutes beans were tan, turned TO to 437, BT was increasing past 350
First pop of 1c started at ~12mins, BT was 395-400 and ET was 470 - turned TO down to 415
1c was going strong until ~15 minutes, BT was ~406-410 and ET 462
At 19 minutes I heard first snap of 2c - BT was 426 and ET 462
Pulled beans and immediately cooled
By sight and sound (barely 2c) I'd think beans were city+ to full, but bean temp was only 426, wouldn't that be more of a city than city+??? I'd appreciate any advice - finally finished the 37 pages of posts in the SC/TO profiles thread (took several evenings of perusing). Some stuff I read there is the reason I took the beans more slowly thru drying and tried to keep them at ~350f for 3-4 minutes.
Below should be pics of the roasted beans, the TC placement (1 under the spacer ring and 1 over), and my leaf blower-colander bean cooler that sucks air down thru the beans and cools them to touch in ~15 seconds