# Instrumenting a Small-Batch Tea Roaster

## Batch Control

A small-batch tea roaster behaves more like a lab oven than a coffee roaster: the thermal mass is low, the leaf is fragile, and a 10 °C overshoot can turn floral oolong into flat toast. For a 1-2 kg drum, the most useful control loop is not aggressive PID automation, but repeatable heat input with tight operator feedback.

## Sensors

Our setup uses two K-type thermocouples: one in the exhaust stream and one lightly shielded near the leaf bed. Exhaust temperature responds quickly to burner changes, while leaf-bed temperature lags but tracks the actual roast curve better. Logging both at 1 Hz gives enough resolution to spot stalls without drowning the operator in noise.

```yaml
roast_profile:
  tea: "high-mountain oolong"
  batch_weight_g: 1200
  charge_temp_c: 145
  exhaust_limit_c: 165
  target_duration_min: 18
  fan_percent: 42
  drum_rpm: 34
```

## Process Notes

The first five minutes are mostly about driving off surface moisture without scorching edges. After that, aroma changes become more useful than color: grassy notes give way to steamed greens, then toasted grain, then light honey. The operator should reduce heat before the desired aroma peak, because the drum and exhaust path continue feeding energy into the leaf.

## Reproducibility

The most valuable data is not the final temperature, but the shape of the curve and the context around it. Ambient humidity, rested leaf moisture, airflow setting, and unload time all affect the result. A good roast log makes the next batch easier to correct instead of pretending every run starts from identical conditions.

## Practical Takeaway

For small-batch tea roasting, precision comes from simple instrumentation, disciplined logs, and conservative heat changes. Automation can help, but it should preserve the roaster’s sensory decisions rather than hide them behind a recipe button.