I have during the last months noticed that my 1Cs (First Crack Start) temps have drifted from what I consider normal (198-202C/388-395F) up to 202-208C/395-406F. I have recently put in a new BT TC (from Mr. Li) as I did get some misreadings and dropouts (short circuit?) from the original one. This was worrying me so I decided to rip the roaster apart and check the TCs.
I did this "calibration" with my Center meter (though I use a Phidget 1048 with Artisan). I also had a small thermometer (digital "stick") and one of the probes that came with the Center 301. Well, long story short, all of the probes (including the suspected faulty one that I replaced) did read within 1.5C/3F in both ice-water and boiling water. (The readings were also "correct" at 0.5C cold and 99.5C hot at sea-level.)
I took a look at the blog that Cropster posts from the current World Roasting Championships, where their 1Cs seems to be at 192-193C/378F, which I would also consider "off", but I also noticed an even greater "deviation" (1Cs at 188C/370F), when I was watching the Swedish Championships. (The current WC in Shanghai is done on a Geisen, while the Swedish Champs was done with a Diedrich.)
Have I learnt anything? Well apart from that my roaster was somewhat dirty and needed cleaning
, TCs are "relative". As long as the temp values are consistently "off", i.e always off by the same value with the same charge weight of the same beans, I do get enough indication of what is going on. I actually think that it's somehow good that this started to happen, as I got to pay more attention to what was going on with the roast and less on the computer. There are a lot of nice smells and aromas going on throughout the roast.
I.e I use the trowel a lot more, trying to associate differerent smells with different points on the roast curve. (What Willem Boot calls "Sensory Mile Stones". Check Youtube...)
