BT RoR guidance for popcorn poppers and small fluid bed roasters? - Page 4

Discuss roast levels and profiles for espresso, equipment for roasting coffee.

#31: Post by Trjelenc »

So assuming someone is trying to keep a reasonable rate of rise (adequately keeping their heat and fan under control) during the development, THE single glaring problem of going off of a DTR target to end your roast is that you end up assuming that if the roast before 1C goes quicker, you should run the development shorter, or if it goes slower, you should run the development longer.

Example: you have a roast that goes through the first 2 phases in 5 min and 3 min, so at 8 min you hit first crack and you know you want 20% DTR so you end the roast at 10 minutes.

Next time you end up getting to yellow in 3:30 and another 3 minutes to first crack (FC @ 6:30), so you allow it to run 1:35 and end the roast around 8:05 once you hit around 20%.

So maybe this example is a bit of an extreme difference in roasts, but basically you had a roast that was 1:30 quicker in the green phase (might even cause no flavor impact), the same middle phase, and the DTR tells you to compensate for that by... shortening the length of your development?

minus1psi (original poster)

#32: Post by minus1psi (original poster) »

To me, the newbie in the peanut gallery, the scenario you described is the exact reason I wish I could use DTR! I have made assumptions about your roast scenarios:
  • same green coffee in both roasts
  • same amount of coffee in each roast
  • the meaningful variable is the application of energy to the roasts
There are many times when I wish I was articulate and this is definitely one of them. Please try to glean what I mean even if the words fumble the concept. To repeat my disclaimer, this is from a newbie. The underlying thought is that similar amounts of energy absorbed by the beans should result in similar amounts of roasting. If one roast you got to yellow in 5 minutes and another roast got there in 3:30, it seems right to figure the second roast was hotter and applied the energy necessary to get the beans to yellow in less time.

Similarly if the first roast got you to 1C in 8:00 minutes and the second roast got you there 6:30 minutes, it would seem that the beans absorbed the same amount of energy in less time in the second roast. Why wouldn't the second roast complete development in less time? That is exactly why I want DTR to work, to help predict when the beans will have absorbed the energy needed to complete a roast.

Then this gets into an area where I do not have any interior model to rely upon -- roast momentum. Presumably your second roast goes into 1C with more momentum than the first roast. I say presumably because in your examples the two roasts both took the same amount of time to go through the second phase (3 min). Since roast #2 was hotter and reached green in less time, I would intuit that the energy was reduced at some point to allow it to spend proportionally more time in the second phase.

How does reducing heat on a roast that had high early momentum affect the overall momentum of the roast and in what way... no need to ask me, I don't know.

It would be great if I could rely on DTR to compensate for major adjustments in the application of energy pre- and mid-development but that does not seem likely. My hope is that if I can successfully wrestle techniques for controlling a roast, it will become part of a reliable metric for dropping the beans at a nearly identical point from roast to roast. I do currently hope to rely on it to compensate for major changes in application of energy but rather to fine tune my understanding of the moment a roast is ready to drop, but my roasts are nowhere near that point of consistency yet.