# Instrumenting a Small-Batch Tea Roaster

A small-batch tea roaster is closer to a lab instrument than a kitchen appliance. At 2-5 kg per run, the operator has enough thermal mass to build repeatable roast curves, but every airflow adjustment, drum speed change, and heat input still shows up quickly in the cup.

## Sensors and Control

The core instrumentation is simple: one thermocouple in the bean mass equivalent, one in the exhaust stream, and a differential pressure sensor across the fan path. The roaster controller samples at 1 Hz, smooths the thermocouple readings with a short moving average, and logs operator events such as charge, turn, aroma shift, and drop.

```yaml
roast_profile:
  batch_size_g: 3000
  drum_rpm: 42
  airflow_percent: 65
  target_drop_temp_c: 118
  max_rate_c_per_min: 9
```

## Heat Transfer in Practice

Tea is less forgiving than coffee because the target temperatures are lower and the aromatics are more fragile. A good oolong roast might spend most of its time between 85 C and 115 C, where radiant heat, airflow, and moisture migration matter more than brute burner power.

## Repeatability

The most useful metric is not final temperature by itself, but the relationship between exhaust temperature and leaf temperature over time. When those two traces separate too quickly, the roast often tastes flat or baked; when they converge gradually, the batch tends to preserve florals while gaining sweetness and body.

## Lessons From Production

After a few dozen batches, the roaster's job becomes less about chasing a perfect curve and more about maintaining stable starting conditions. Preheat time, drum soak, ambient humidity, and even how long the leaf rests after sorting can shift the first ten minutes enough to require a different heat schedule.