What's a reasonable Bullet roast curve?

Roasting on the Bullet
1

I just got a Bullet R2 and I’m new to roasting on a Bullet (coming from a Behmor), so in prep for this I’ve read a lot about roasting online and from authors like Scott Rao. In learning about roast curves, I understand now that commercial roasters use ET/BT while we only get BT, since Aillio chose not to give use ET data. Even without the traditionally expected data, I would think that we should still see smoothly descending ROR curves from our BT sensor, but I’m not seeing in many roast profiles on Roast.World where the Bullet ROR curve descends particularly well. A lot of them seem to peak, descend, and then level out toward the middle/end. Here’s an example of one I was looking at. I have this same blend and want to roast it on the Bullet, and the numbers for this profile look good but the curve seems flat in my opinion:

I’m trying to learn how to do it properly, but I’m 5 lbs in (after seasoning roasts) and so far my roast deltas are 30-40 AgTron points, so obviously I’m doing something wrong. I also recognize that ROR curves are not one-size-fits-all and there will be variations with different roasters and different beans, but with each roaster there should be a reasonably expected curve that will result in a good roast (excluding edge cases) and I want to understand that about the Bullet.

Main questions:
Is a smoothly descending curve—like those that commercial roasters often present as ideal—something I should expect when roasting on the Bullet, or should I anticipate my ROR curves leveling out toward the end?
Does the Bullet behave similarly to large commercial drum roasters, so that best practices aimed at machines like a Probat can generally be applied to the Bullet?

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This isn’t just a function of IBTS vs BT ROR curves, or roaster preferences or habits-- it’s a matter of models that are physically (and mathematically) impossible to execute for certain combinations of roast color/end temp, first crack times, and development times.

There are people who assert that this is not a worthwhile target to pursue. It’s based on anecdotal evidence from a consultant (Rao) who sells his expertise, and a key component of that package is the “smoothly declining ROR.”

The most important thing is cup quality, which is 100% subjective. The factors that contribute to that, based on reproducible evidence, are, in rough order of descending importance:

  1. Green bean quality
  2. Roast degree (color + internal development)
  3. Application of heat over time (heat plan)
  4. Development time (time post first crack)
  5. Time to first crack
  6. Other factors like fan, drum speed, etc.

The problem is, a “smoothly declining ROR” is mathematically impossible for certain combinations of FC time, development time, and end temperatures. You physically (due to physics, and math) cannot construct a smoothly declining derivative of the time temperature curve when, for example, you want to control all three of time to first crack, end temp, and development time for many reasonable constraints.

So, in order to get a smoothly declining ROR, you have to buy in to a set of postulates that constrain how dark you can roast coffee and/or how quickly you can roast it, and roasting it more quickly (all other things being equal) definitely impacts internal development and overall flavor in the cup.

If that works for you, great. Otherwise, experiment , taste, repeat.

More reading, and a free course here: Learning - #4 by gilbertwilliamson.db

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That makes complete sense, especially given that it’s ultimately down to physics and math, and there’s no way to make them conform to any ruleset outside of the laws of physics.

Application of heat is my biggest struggle right now. I really don’t know when to apply heat or how much; my last couple of roasts seem to have plateaued right after first crack, which makes me think I started stepping my heat down too early in the roast. I just registered for that course to soak up some more knowledge. Will it discuss heat application?

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Yep, for sure. There’s a self-guided experimental portion where you get to learn to control the heat inputs to get the desired outcome.

Once you learn to drive the roaster, you can target different outcomes and decide which ones work for you.

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