Like many, adding thermocouple probes to my roaster was one of the first modification I made. When I contacted Eric I believe he was out of the original BT probe adapter, so we improvised. We came up with the "Alternate BT Probe Location." I've been using that location for a while, but got my hands on the adapter and probe for the original location. Below is a comparison of the two.

Blue: Original BT Probe Location
Red: Alternate BT Probe Location



Here is a high-res picture of the graph



Here is a high-res picture of the placement

My observation is the Alternate BT Probe Location is more finicky. It does not give as an accurate measurement for BT. Although it is covered by beans it is lower than their real temp. This becomes really apparent in later stages of a roast. The Alternate BT Probe Location will hit 1st crack anywhere between 186-190 and 2nd at 205. The one roast I took 2nd crack today give a more common 28C difference between 1st and 2nd crack when using the Original BT Probe Location. I'll be sicking with the Original BT Probe Location from here on out.

Thought I'd share my experience with the two.

Valuable info. I've got my BT probe in the original location and the MET up by the bean chute. I'd been wondering about the alternate BT location. Thanks for doing the spade work, Paul.

Thank you for doing this. It does add clarity to some issues, but to be more valuable, info wise, is if they were identical thermocouples, just in the two different locations. If one's even slightly denser than the other, or a slightly different design, then we can't draw a conclusion about which BT location is more "accurate BT". For all we know, this graph could just be telling us how the two different probes are absorbing heat. Especially since they are both essentially tracing along the same line shape for the most part.

It would make more sense if the probe that was completely buried in the bean mass as well as closer to the heat source ( alternate BT) that it would register a higher temp, especially towards the end, but it's not, it's showing the exact opposite.

TomC wrote:It would make more sense if the probe that was completely buried in the bean mass as well as closer to the heat source ( alternate BT) that it would register a higher temp, especially towards the end, but it's not, it's showing the exact opposite.

I know. It does not make sense. I really thought it would be a better placement, but it's not in my experience. It would be interesting to use a 1/8 probe for the alternate location, but I don't think it's even possible. It would still not have as much of a penetration into the bean mass.

The lower location is more influenced by the voids created as the vanes turn, and may not be good spot for getting an averaged reading. The best spot is almost always where the heat flow leaves the bean mass, since this is most correlated to the average temperature of the bean mass as a whole. On the Quest, the stock location is quite good in this respect.

However, in this case, the readings are so highly correlated that it makes no real difference which one you use; you just need to recalibrate your bean temperature signposts. to suit the new reading.