Introduction
This note captures what changed after replacing the heater in the Gene Café CBR-301, and how the system was recalibrated using real roasts.
It is not a theory piece.
It is based on:
- Roast 70–79
- Controlled use of a single variable (TRT)
- Weight loss as the validation output
The goal is simple:
understand how the machine behaves now, not how it behaved before
What Triggered Recalibration
The first roasts after the repair appeared to confirm a problem.
Early results (Brazil)
- 13:05 → 12.5% weight loss
- 12:35 (warm) → 13.7% weight loss
These are materially lower than expected.
At this point, it looked like the machine had become underpowered.
That interpretation was incomplete.
What the Data Actually Showed
The recalibration sequence moved from Brazil to Honduras and then to a washed Colombian (Regional Jess).
Honduras (Roasts 72–75)
- 15.5% → 16.5% → 14.6% → 15.7%
These roasts demonstrated something important:
the machine is still capable of reaching full development
This ruled out a simple “loss of power” explanation.
The Clean Signal, Regional Jess
The most useful data came from repeated warm roasts on a single washed Colombian.
Key roasts
- 12:55 → 11.8%
- 13:20 → 16.0%
- 13:30 → ~16.5–17%
This is a very strong response curve.
A small change in TRT produced a large and predictable change in weight loss.
The Core Insight
The heater replacement did not break the system.
It changed how clearly the system expresses the coffee.
Before repair
- Behaviour was more buffered
- Different coffees produced similar outcomes
After repair
- Behaviour is more transparent
- Coffee characteristics show up more clearly
What Actually Changed
The relationship between TRT and weight loss is still valid.
However:
it is now more sensitive to both time and coffee type
This shows up in two ways:
- Small changes in TRT have a larger effect
- Different coffees separate more clearly in behaviour
The Fan Behaviour
The change in fan step timing was real and visible in the data.
Before repair
- Fan step ~4 minutes
- Around 200–210°C
- Useful as a phase marker
After repair
- Fan step occurs much later
- At higher temperatures
- Sometimes near the end of the roast
The correct interpretation is:
fan behaviour reflects system heat, it does not control it
It is now a diagnostic signal, not an anchor.
The Working Model After Recalibration
The roasting approach has not changed.
TRT remains the only control variable
Fan, temperature adjustments, and drum speed are not used as active controls.
The system is:
- set TRT
- run the roast
- validate with weight loss
New Anchors
Warm, washed coffees (Honduras, Regional Jess)
- 13:20 → ~16% weight loss (centre)
- 13:30 → ~16.5–17% (upper bound)
This is the primary working range.
Cold, washed coffees
Derived from observed offsets:
- ~13:40–13:50 → ~15.5–16.5%
Naturals (Brazil)
Naturals now behave differently to washed coffees.
- Lower weight loss at the same TRT
- Require slightly longer roast times
Approximate adjustment:
- +10–20 seconds vs washed
Decaf
Decaf remains a separate system.
- Faster early behaviour
- Lower overall weight loss
Typical working range:
- ~12:30–12:50 (warm)
What This Means
The system is now:
- stable
- repeatable
- more sensitive
The key change is not capability.
It is visibility.
the machine now shows more of what the coffee is doing
Final Position
The recalibration confirms three things:
- TRT remains a valid and sufficient control variable
- Weight loss remains the most reliable validation signal
- Coffee type must now be accounted for more explicitly
Summary
TRT-only roasting remains valid
The machine is not weaker
The system is more responsive
Calibration required ~+20 seconds for washed coffees
Fan behaviour is no longer a control signal