Total roast time and weight loss are the most reliable way to understand and control roast outcome on the Gene Café CBR-301.
This is not because they are precise. It is because they are consistent.
Once the behaviour of the machine is understood, time becomes the primary control, and weight loss becomes the validation of what actually happened.
The relationship
Roasting is not about reaching a specific temperature. It is about how much energy is applied over time, and how the coffee responds to it.
On this system, that relationship can be understood simply:
- Total roast time (TRT) defines how long energy is applied
- Weight loss (WL) reflects how much change actually occurred
Together, they form a reliable way to move from intention to outcome.
[Insert Diagram — TRT → Weight Loss → Outcome]
Total roast time (TRT)
Total roast time is the moment you stop the roast — when cooling is initiated.
It is the single most controllable variable available on this machine.
Holding everything else constant, changing total roast time will consistently move the roast outcome.
However, the same time does not always produce the same result.
Start temperature, airflow behaviour, and bean characteristics all influence how that time is translated into actual development.
Time is control — but not certainty.
Weight loss (WL)
Weight loss is the difference between green and roasted coffee weight, measured at the start of cooling.
It reflects how much moisture and volatile material have been driven off during the roast.
Unlike temperature or crack sound, weight loss directly captures what physically happened to the coffee.
It is not predictive — it is confirmatory.
Weight loss tells you where you actually landed.
How they work together
Total roast time is the input. Weight loss is the result.
If two roasts share similar conditions, then:
- Longer total time generally leads to higher weight loss
- Shorter total time generally leads to lower weight loss
But this relationship is influenced by:
- Start state (cold vs warm machine)
- Airflow changes (fan step timing)
- Bean density and processing method
This is why weight loss is used to validate time, not replace it.
Structural ranges (current working model)
Across repeated roasts on this system, weight loss has begun to align with broad structural outcomes:
- 14–15% → balanced, medium structure
- ~16% → fuller, more developed structure
- ~17%+ → upper guardrail, potentially heavy or fatiguing
These are not fixed categories. They are working reference points.
Different coffees will land differently within these ranges.
What matters more than expected
- Total roast time consistency
- Time to key points (especially ~200°C)
- Airflow behaviour around the fan step
- Repeatability across similar roasts
What matters less than expected
- Exact temperature values
- Crack sound alone
- Small timing differences without context
Practical use
After each roast, compare intention to result:
- What total time did I target?
- What weight loss did I achieve?
- Did that match the structure I expected?
If not, adjust the next roast through time, and validate again through weight loss.
This loop — time → outcome → adjustment — is where consistency comes from.
What this replaces
This approach replaces the need to rely on:
- Exact temperature targets
- Crack timing as a primary control
- Assumptions about roast level based on colour alone
It does not remove uncertainty, but it reduces it.
Closing
This is not a model of precision.
It is a model of control and validation.
Total roast time sets the direction. Weight loss confirms where you arrived.
Everything else sits around that.
Next: Returning to the curve — applying this in real roasts
Coffee | One Roast at a Time — oneroastatatime.com
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