If you have no hōroku, the earthenware pan made for roasting tea, a frying pan will do. Over a low flame, stirred with a wooden spatula, the leaf changes colour and so does the smell of the room. The trouble is knowing where to stop. You want light, medium and dark, but the kitchen holds no ruler for the three.
How do you roast three levels at home, and what makes them three?
The time. Keep the pan, the weight of leaf and the flame the same all three times, and move only the length before you stop. Do not turn the colour into a number: put the three on one sheet of paper and photograph them together in the same light. That is how the Kochi trial was set up too — the temperature held, the time in the machine moved.
Colour is a usable guide
Colour has been checked as a usable guide. The 2020 report from Ishikawa, seen in “Tea roasting temperature: what 180°C, 200°C and 220°C actually measured”, roasted stem tea at 180, 200 and 220°C, measured the colour of the leaf itself, and writes that the path traced by the three values L*, a* and b* is the same whatever the temperature. The same report, though, recommends watching L*, the lightness, and b*, the yellowness, rather than a*, the redness. L* rises at the start of roasting before it falls, so watching the lightness alone will confuse a barely roasted leaf with a far-advanced one. That is what putting the three on one sheet is for.
Colour figures move with how they are taken
The absolute values move with how they are taken. The Kochi trial ground the hojicha to a powder before reading the colour, and a* in first-flush tea came out at 1.34 for the light roast and 5.11 for the dark (Table 4 of the same report, 2014 data; the samples whose colour was measured were made in two levels, separately from the three levels of 2013, the dark one at 10 revolutions). Ishikawa measured whole leaf. The maker of the colorimeter was the same, and grinding or not still moves the figures. Not putting a number on it at home is less about lacking the tools than about a number made at home travelling nowhere. What changes when the thing roasted is stem rather than leaf is chapter 7.