# Building a Small-Batch Tea Roaster

Small-batch tea roasting requires tighter control than a conventional kitchen oven can provide. A practical benchtop roaster starts with a 1–2 kg stainless-steel drum, a variable-speed gearmotor, and an insulated heating chamber. The rotating drum keeps leaves moving so that radiant heat does not scorch their edges, while a removable chaff screen prevents debris from reaching the heating elements.

## Temperature and Airflow Control

The most useful measurements are inlet-air temperature, exhaust temperature, and leaf temperature. Type-K thermocouples are inexpensive and tolerate roasting conditions well, but the leaf probe must extend into the moving bed without contacting the drum. A small centrifugal fan with a damper provides repeatable airflow, carrying away moisture early in the roast and volatile compounds during finishing.

## Control Loop

A microcontroller can sample the thermocouples and drive a solid-state relay using a conservative PID loop. Heater output should be capped during the final minutes because dry leaves respond quickly to radiant heat. The following configuration is a reasonable starting point for a 500 g batch, though every drum and tea style requires tuning.

```yaml
profile:
  preheat_c: 120
  ramp_c_per_min: 8
  finish_c: 145
  finish_hold_sec: 90
  drum_rpm: 42
  airflow_percent: 60
```

## Roast Profiling

A typical cycle begins with a stabilized preheat, followed by charging the drum and applying a steady temperature ramp. Operators should log temperature, heater duty, airflow, and aroma observations every 15–30 seconds. Green oolong may need a gentle ramp to preserve floral notes, while heavily oxidized tea can tolerate a hotter finish that develops toasted sugar and nut aromas.

## Safety and Maintenance

Tea dust is combustible, so the roaster needs thermal cutoffs, grounded metalwork, and an emergency stop that disconnects heater power independently of the controller. After each session, vacuum the chaff collector and inspect the exhaust path. Periodically verify probe accuracy in boiling water and check the drum bearings, motor coupling, and relay terminals for wear or heat damage.