mpdeem wrote:Thanks for posting the photos. Regarding the placement of the BT thermocouple...looks like it is situated in one ofheat vents - is that correct? If so, would that mean it reads the evironmental temperature of the heat vent...as opposed to the bottom secton of the bean mass?

I have always wondered how best to obtain 'bean temperature'. Right now I have only one temperature probe - a kitchen dial mounted in the lower third of the roast chamber, mounted through a drilled hole in the side of the roaster. The probe runs midway across the chamber in an effort to capture the temperature of the lower third of the bean mass.

I have noticed raw bean volume influences the probe accuracy at 1st Crack and maillard onwards. The larger the bean volume, the less accurate the temperature dial appears to be during 1st Crack and maillard in that the bean color, behavior (cracking, movement) often indicate higher temperatures than the dial.

I am wondering if your placement of the probe in the heat vent might provide a more accurate reading..or at least one less influenced by bean mass?

I haven't used the popper setup in maybe 10 years. The blog was back at the end of 2009. I continued to tweak and improve it, but eventually moved to an highly modified alpenrost to get a larger batch size, it could do about 1/2 pound. The alpenrost was gutted so I could monitor ET and BT, and control the heater and drum motor. Basically I did a brain transplant on it. Then I retired from roasting, but may start again one of these days.

So for the pics above, there is one probe right where the hot air enters the roast chamber. That tip of the probe is shown in the 2nd and third picture, I used that probe for ET when I roasted. PID control was based on this temp. This is a bead thermocouple with fiberglass insulation.

First pic shows the thermocouple (TC) probe I used for BT. Enter the chamber at the top of the Pumper body, going straight across to the middle. IMHO, it did a good job measuring the temp of the bean mass. The temps I measured would correlate close enough to what I expected for first and 2nd crack. I would use BT to figure out the roast profile.
I found the Pumper this morning. Turns out that I had a hole for to angle the TC down into the roast chamber, but I must have decided straight across near the top was better than angled down.

Now that I think about it, for BT placement, I'd load up the Pumper with whatever I decided was the batch size I wanted to use, and do a test roast. Then measure how high the main mass of beans go after first crack. Then estimate the bottom of the mass, and try to center the BT probe in the mass. Figure BT is more important at end versus beginning of roast, and center of the mass will move up as roast progresses.

I had two basic profiles, one for high elevation hard beans, and one for low elevation (island) soft beans.
High elevation would start off at max power, but then would cut back on the power as I approached first crack.
Low elevation I would start at a lower power, maybe 70% but that's a guess. Then cut back even more approaching 1st.
Then I might tweak the profile depending on the results for a particular bean.

For any profile, tried to maximize time between first and 2nd. Typically end roast at start of 2nd.

I started off with a variac, but I had trouble with control and repeatability, so moved to a PID and SSR to control the heat.

My roast size was always the most I could do, based on the Pumper airflow and moving the beans at start of roast. Never experimented with roast size because I could control heater power and fan power.
The large size may have had the unintended consequence (or maybe i meant it do it lol) of keeping the beans closer together. Larger batch size and they don't move as much, or as high.

Randy

minus1psi wrote: With a single TC for BT, I think I would go in through the exposed plate in the bean column area rather than fabricate a saddle over the top of the chimney.

That makes sense, I would try to put any TC into the pumper instead of the stack .

With my setup, to end a roast, I turned off heater and fan power, pulled off the stack, and then I had enough slack in all the wiring to lift up the pumper body and dump the beans. Was quick and relatively easy.

Assuming you're using type k TC's, you can pick up special connectors that use the same metal as in type k wires.

I bought the flat pin type from mcmaster https://www.mcmaster.com/type-k-thermoc ... onnectors/ years ago. Worked fine for me. Then I marked both ends for polarity to make it easier to connect because my eyes are old and didn't have great lighting.

My other advice is just do it. Monitoring BT is a minimum requirement, IMHO, for roasting. There are inexpensive meters that read a TC. Small hole in the pumper, TC meter, and a TC probe and you're set.

Randy