Without a clay roaster, a frying pan will roast tea leaves. Move them with a wooden spatula over a low flame and the colour shifts, then the smell of the room. The hard part is knowing when to take the pan off the heat. Three stages are the aim, but no kitchen comes with a yardstick for them.

This piece looks at what to divide the three stages by, and how to keep a record of the colour.

Change only when it stops

The leaves begin to rustle at the tip of the spatula. The three stages are divided by the time before the pan comes off the heat.

The pan, the amount of leaf and the flame stay the same all three times. Only the length of time before stopping changes. A prefectural station's trial was built the same way, holding the temperature and changing the time in the machine.

The sources show that the same design works at home. Once the stages are set by time, the colour is next.

Colour can be the yardstick

Set the three side by side and the colours run from a light brown to a deep one. That colour is a fair guide has been checked.

It is like a hillside turning in autumn, from the foot upward. A report from another prefecture found that whatever the temperature, the leaf's colour moved along the same path. The same report advised watching lightness and yellowness rather than redness.

Lightness rises briefly at the start of roasting and then falls. Judged by lightness alone, early leaf and well-roasted leaf can be mistaken for each other. The sources show that laying all three on the same paper is enough. A photo under the same light keeps the colours as they are.

Numbers move with the method

It is tempting to turn the colour into a number, but no kitchen has the instrument. Even if it did, the number would not travel beyond the house.

The prefectural station ground the tea to powder before measuring; the other report measured whole leaf. The instruments came from the same maker, yet grinding alone moves the figures. No line can be drawn at the number where dark roast begins.

The sources show that a colour reading belongs to the way it was taken. The figures and conditions come together at the end.

The numbers in detail

Trial design
Holding the temperature and varying the time follows the trial by the Tea Experiment Station of the Kochi Agricultural Technology Center.
Stem tea colour
Ishikawa's 2020 report roasted stem tea at 180°C, 200°C and 220°C and measured the colour of the leaf itself.
Colour path
At every temperature, the three L*a*b* values followed the same path.
Values to watch
The same report advised watching lightness L* and yellowness b* rather than redness a*.
Colour values
The Kochi trial ground the tea to powder before measuring. First-flush a* was 1.34 for light and 5.11 for dark (Table 4, 2014 data).
Separate samples
These colour samples were made apart from the three-stage 2013 samples, in two stages, with the dark roast at 10 revolutions.