Posted by: Andre | November 13, 2009

Roast Profiling

Shortly after developing the custom PID on the Arduino I started work to adapt the Processing part of it to be able to plan a roasting curve. A number of changes are needed to make this possible:

  1. Changing the logging time frequency and graph scale
  2. Add data logging capabilities – I settled on a 2 second time logging and graphing interval
  3. Add ability to have a planned curve
  4. Add input controls to restart graphing and begin logging when beans are dropped in the roaster
  5. Add input controls for logging start and end of First Crack as well as the start of Second Crack

No new hardware or calibration was actually necessary, I’m using the same PT1000 probe as in my Caravel to measure water temperature seen here:


Next you can see my first roast using this method of Yemen Mokha Harasi, on this roast 1C started at about 9 minutes and 180C and terminated 5 minutes later just at first snaps of 2C. Orange line is planned graph (since this was the first it was off by quite a bit) and the blue line is actual.

Yemen Mokha Harasi #1

My next roast I’m going to try to change this profile from a quick ramp at the beginning to more of a drying soak phase to start with. This should give the profile shape up to first crack more of a concave shape rather than convex. Something like this is planned now:

Planned roast profile

This gives about a 3 minute soak period, then a quick ramp to 1C at 8 minutes, and then 2C 5 minutes later for a 13m total roast time. The benefits of a profile like this are often said to make the coffee much more interesting in terms of flavors, where as the other profile I started with is more muted by comparison. I’ll have to just roast and see for myself. For now the previous roast cupped nicely, and came out well as espresso to me. More to follow in another post about the cupping session along with impressions on it as espresso.

The great thing about this setup is that the Arduino itself needed no new programming, and I can switch between roasting and brewing applications at any time.


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