# Instrumenting a Small-Batch Tea Roaster

Small-batch tea roasting rewards precision because leaf mass, residual moisture, and airflow change quickly at 300-800 gram scale. In our 600 g rotary drum roaster, a 10-15 second delay in heat response can be enough to flatten aromatics in oolong or push green tea into toasted-grain territory.

## Sensors and Control

The roaster uses a K-type probe near the drum wall, a second probe in the exhaust stream, and a low-pressure differential sensor across the chaff screen. Leaf temperature is inferred rather than directly measured, so the controller tracks rate of rise, exhaust humidity, and fan speed together instead of treating drum temperature as the only source of truth.

```yaml
profile:
  batch_g: 450
  preheat_c: 118
  fan_percent: 42
  phases:
    - { name: dry, target_c: 92, ramp_c_per_min: 7.5 }
    - { name: aroma, target_c: 116, ramp_c_per_min: 3.0 }
    - { name: finish, target_c: 122, hold_s: 55 }
```

## Profile Design

A good roast profile starts with the tea, not the machine. Rolled oolong tolerates a slower finish because the leaf opens gradually, while delicate green tea needs lower exhaust temperature and more airflow to avoid trapped steam. We log every batch with ambient humidity, starting moisture, charge weight, and a five-minute sensory note after cooling.

## Practical Results

The biggest improvement came from controlling airflow before changing heater power. Higher fan speed during the drying phase reduced grassy notes, but too much airflow late in the roast stripped floral aromatics. With repeatable profiles and basic telemetry, the roaster became less of a guessing exercise and more like a small thermal system that still leaves room for taste.