Context
Roast 27 was designed as a TRT (Total Roast Time) validation test.
The working assumption was:
Cooling at ~13:30 should consistently land near ~16% weight loss.
Roast 26 had previously landed at 16.2% using a 13:30 hard stop.
Roast 27 was intended to confirm whether TRT alone is a reliable operational control.
Parameters
- Batch size: 250g
- Set temperature: 250°C
- No preheat
- Cooling initiated: 13:31 (811 seconds)
- Weight out: 207.4g
- Weight loss: 17.0%
- Ambient start temp: 23°C
No crack flag recorded.
Machine Behaviour (Corrected JSON)
Early Phase
- Fan OFF → 2 at start
- Fan 2 → 3 at 3:45 (225s)
- Temperature at shift: 198°C
This fan transition occurred earlier than the established system median (~4:05–4:10) and at a lower bean temperature (~202°C is typical).
Fan remained at 3 for the remainder of the roast.
Temperature Milestones
- 100°C → 0:51
- 150°C → 1:53
- 180°C → 2:53
- 200°C → 3:49
- 230°C → 7:04
- 240°C → 8:59
- 245°C → 9:47
- 250°C → 11:12
Final phase was stable (≈247–249°C average in last minutes).
No oscillation or stall observed.
Observational Notes
- Visibly darker than Roast 26 (16.2%)
- Even development across batch
- No surface oil observed at logging
- Slightly more pronounced seam expansion
- Colour saturation clearly deeper than 16.2% reference
This roast sits structurally above 16.2% and below the 17.8% Topazio upper guardrail reference.
Primary Outcome
13:30 TRT is not a precision WL control.
Roast 27 landed at 17.0% WL, despite matching total time from Roast 26.
The material difference appears to be:
Earlier fan 2 → 3 transition at 3:45 (198°C)
Compared to prior roasts, this represents:
- ~20–30 seconds earlier airflow escalation
- Occurring below the typical 200–202°C transition cluster
That earlier airflow shift likely altered the energy balance across the roast.
Structural Interpretation (Carefully Framed)
Earlier fan shift means:
- Earlier increase in convective airflow
- System compensates thermally
- Drying phase pacing shifts slightly
- Cumulative energy distribution changes
Even with identical TRT, the roast trajectory was not identical.
Conclusion:
Airflow timing is a primary structural variable on this system.
TRT functions as a ceiling — not a guaranteed WL target.
What This Roast Adds to the Santos Map
Current structural markers:
- 15.0% — lower comfort band
- 15.5% — mid comfort band
- 16.2% — upper comfort
- 17.0% — upper structural reference (Roast 27)
Roast 27 becomes the meaningful high-band Santos reference under current airflow behaviour.
It is not a mistake.
It is a data point.
Learning Summary
- Weight loss remains the primary anchor.
- TRT alone cannot guarantee WL precision.
- Fan transition timing materially influences outcome.
- Ambient temperature may influence early system behaviour.
- The Gene Café is consistent — but airflow timing changes matter.
Status
Resting prior to structured espresso comparison with Roast 26 (16.2%).
Roast 27 is designated as:
Upper structural reference for Brazil Santos under early fan-shift conditions.
Further evaluation pending espresso testing.