Guide
This guide exists to capture what has stopped changing.
Milestones are recorded as patterns stabilise. The first appears below after 20 roasts.
It isn’t a complete manual, and it isn’t meant to be read end to end. It’s a place where patterns that repeat often enough, across coffees, roasts, and mistakes, are written down once they feel stable.
Everything here started life elsewhere, usually as uncertainty.
How this guide is built
Most of the work on this site happens in the Notes.
Notes are where individual roasts are logged, questions are explored, and assumptions are tested. Over time, some of those questions stop feeling urgent. When that happens, the understanding they leave behind is distilled and recorded here.
If something isn’t in the guide yet, it’s usually because it hasn’t earned the confidence to be.
How to use this guide
This guide is not prescriptive.
Nothing here should be treated as a rule, a guarantee, or a best practice. It reflects what has worked consistently enough on a single setup, with a limited but growing range of coffees.
Some sections may feel obvious. Others may feel incomplete. Both are fine.
If you just want to roast and drink coffee, you don’t need to read any of this.
What you’ll find here over time
As patterns repeat, this guide will gradually include:
- How decisions are made when signals are ambiguous
- What tends to matter more, and less, than expected
- How different coffees respond to similar treatment
- Simple reference approaches for repeatable, drinkable results
Nothing is added quickly. Nothing is fixed permanently.
Crack audibility on naturals (what stopped changing)
Across multiple natural coffees roasted on the same Gene Café system, first crack proved to be coffee dependent rather than system dependent. Brazilian naturals consistently produced quiet or smeared crack behaviour, even when development was sufficient, making time, colour, aroma, and weight loss more reliable decision anchors. An Ethiopian natural later demonstrated that clear, rolling crack could return without any system change, confirming that airflow and exhaust were not suppressing crack universally. A subsequent Honduras Catuai natural further refined this understanding by producing a clean, audible crack at the lowest development level recorded, showing that crack audibility does not imply deeper roast development. Taken together, these roasts establish that first crack is descriptive, not decisive, and that on naturals, especially under active exhaust, roast decisions are best bounded by structural cues rather than sound alone.
Milestones
After 20 Roasts
After 20+ Roasts
Gene Café CBR-301 Milestone Synthesis
As of Roast 21 (19 full roasts and 2 sample roasts), this page records what appears to have stabilised.
This is not a conclusion.
It is a checkpoint.
Scope
Included in this milestone:
- 19 full 250g roasts
- 2 small sample roasts
- Washed and natural processes
- Central America, Brazil, Ethiopia
Machine baseline:
- Gene Café CBR-301
- 250g batch
- 250°C set
- Fan 2 → 3 around 4:00
- No preheat
All roasts logged via JSON.
All weight loss calculated at cool initiation.
What Has Stopped Changing
Thermal Stability
Under fixed parameters (250g / 250°C / fan 2→3), the machine:
- Climbs heat predictably
- Does not crash at first crack
- Maintains positive development momentum
- Produces repeatable total roast times
Across multiple sessions, similar settings produce similar structural outcomes.
The machine is stable.
Airflow Inflection
Increasing the fan around ~4:00 has become a consistent structural pivot point.
Without it:
- Drying feels less stable
- Chaff clearing is slower
With it:
- Roast progression stabilises
- Crack clarity improves
- Development feels more controlled
This step is now part of the working baseline.
Weight Loss as Structural Anchor
Weight loss has proven more reliable than:
- Crack sound alone
- Total roast time alone
- Visual colour alone
Across 20+ roasts:
- 14–15% WL → balanced medium structure
- ~16% WL → fuller structure
- ~17%+ WL → upper guardrail, potentially fatiguing
Weight loss is currently the most dependable structural reference.
Crack Audibility is Coffee-Dependent
Washed Central Americans:
- Audible
- Clear onset
- Reliable development marker
Brazilian naturals:
- Often muted
- Crescendo less defined
- Crack unreliable as primary signal
Crack is informative.
It is not authoritative.
Coffee-Specific Structural Behaviour
A pattern has emerged:
The Guatemala Caturra Washed blend consistently lands around ~16% WL under ~80 seconds development at 250°C.
This has now repeated across multiple roasts.
In contrast:
Honduras Catuai Washed reached ~14.3% WL under similar development timing.
This suggests structural band is coffee-dependent, not development-time dependent.
Development seconds alone do not determine roast depth.
Pre-crack energy and bean response materially influence outcome.
Repeatability Confirmed
Roasts 18, 20, and 21 (same coffee, same parameters) produced nearly identical structural outcomes.
This confirms:
- Endpoint timing defines structure
- Variation is not random
- The machine behaves predictably
Repeatability now appears stable.
What Has Not Stabilised
The following remain exploratory:
- Intentional movement of a single coffee between structural bands
- Systematic drum speed variation
- Temperature modulation mid-roast
- Multi-variable experiments
These have not yet been explored deliberately.
That restraint is intentional.
System vs Coffee
After 20+ roasts, a distinction is emerging:
System behaviour appears stable.
Coffee behaviour varies within that system.
Early roasts asked:
“Is the machine stable?”
Current roasts are beginning to ask:
“How does each coffee respond to applied energy?”
That is a different stage of learning.
Guardrail Status
Structural bands remain unchanged.
No guardrail has been redefined.
Patterns are observed, not declared.
Any structural reclassification will require:
- At least 3 consistent roasts
- Across at least 2 coffees
Download: Gene Café CBR-301 What I Wish I Knew Before Roast 1
A practical technical reference sheet for new Gene Café CBR-301 users. This free PDF covers safe starting points, airflow awareness, total roast time (TRT), weight loss guidance, and common early mistakes to avoid. Designed to help beginners roast more consistently from day one, without unnecessary variables or wasted beans. Includes temperature references in °C and °F.
Closing Reflection
This milestone is not about declaring mastery.
It is about acknowledging that:
The system is stable enough
to begin asking better questions.
Twenty roasts did not create certainty.
They created clarity.
And clarity is enough for now.