More Bean Mass Probe Experiments – Guatemala Acatenango Gesha

This is the first complete roast profile with the new bean mass probe.  This is 150 g (green) roasted to the beginning of first crack. As for the coffee – the intent here is to get a little darker roast on this bean.  The last batch I roasted stopped between 1st and 2nd crack and was a bit underwhelming.



The bean mass temp is in the light blue.  Directionally this measurement looks OK but there is some strange behavior:

  • The first several readings after the roast started did not rise at all (~71F)  this starting point is about right but the temps should have started to climb quickly.  After touching the TC amplifier board, it started functioning more-or-less as expected.
  • Something similar happened at the end of the roast where the thermocouple appears to be “stuck” continuing to climb after the heater has been turned off.  Again, after touching the amplifier board, it jumped down significantly — but I am not sure the reading is correct. It does appear to be moving in the right direction again.
  • The plot below shows something really weird — the outlet temp and bean mass probes have different periods.  Because the drum rotates, I expect the periodic temperature excursions- I just can’t explain why the periods are different (and not a multiple).  The period of the drum is about 9s.  The period of the bean mass temperatures is about 15s.  The period of the outlet temps is about 9s.  Definitely something going on with the bean mass probe…


This probably has something to do with the way I am capturing temperatures.  Currently the bean mass probe and the other temp probes are not synchronized.  I have the bean mass probe spitting out a temperature every 1/2 second. The Arduino in the Roast Genie triggers a sample of the other probes once per second and triggers the Raspberry Pi to read the serial port from the bean mass probe.  Instead of throwing away the extra data it is queuing up in the serial buffer — this is likely the problem…  Have to make another go of this.


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