TC calibration or ok?

[Agrajag]

Since I've installed my ET TC I've noticed that the BT is overtaking it towards the end of the roast. Also when I preheat, the BT is about 10 degrees warmer than ET at charge temp. Is this normal? At ambient temp they are very similar (within a degree) so I'm inclined to think they are accurate, however with this roast:



the beans look a lot lighter than I would have thought for a 226 degree drop (though I haven't roasted this bean before, it is a brazil but beyond that I don't know any more, I just took a couple of kilos from a mate, they are apparently a few years old, feel quite soft too).

I had the idea to log the fall in temp after roasting, which might give me an idea if the TCs are out from each other at higher temps, but I don't know if the BT will be higher being closer to the drum anyway. Will give it a go next roast anyway, but would like to hear others thoughts.

[edtbjon]

I switched back to solid drum yesterday and made the very same observation. As I didn't go any further than 217C, they became equal at drop point, but would I have pushed any further the BT would have rissen above the ET.
I do have a few houndred "solid" profiles from yesteryear saved but as I hope that I've progressed a little bit in my roasting adventure, I rather look forward than looking at how I did things back then.
For the bean color and also the start of 1C, I guess it's typical of an "aged" bean. I had some Peruvian beans which were past their best going into 1C at 207C (300+ gram charges. The competition Burundi bean had a 1Cs at around 198C in the very same roasting session.). The taste of that Peruvian coffee was much like ... the paper cup it could have been served in... I.e very boring. I don't recall if it was lighter or darker than usual for the drop temp, but Brazils being naturals bean color can vary a lot.

[Agrajag]

Thanks, that's good to know, especially regarding aged beans. I just got these to practise on really, but am pretty happy with the results so will do some more with better beans to get better data (and coffee!)

[edtbjon]

A quick Artisan tip. If you (after the roast) go to Config/Axes... you can change the Max value so that it's say drop-time plus one minute. Then the graph will look nicer and more uniform.

[Agrajag]

Thanks, much better now