Read down the back of a packet — name, ingredients, net weight, best-before date — and the roasting temperature is nowhere on it. The figures are in the industry's own documents. In the appendix to the Green tea labelling standard, two rows sitting far apart, ⑦ and ⑱, carry "roasting: 140°C or above" and "hiire: 70–130°C". Because of those rows, introduced in the opening chapter, 140°C looks like the border.
Where is the border?
Not on the temperature scale. That appendix is not a definition of tea types but a worked list for sorting out who is responsible for the labelling, and it names neither equipment nor place of measurement. A public trial in 1974 called heating at 150°C hiire, and a 1999 study made hojicha at 130°C for 10 minutes.
Time, purpose, evaluation: which of them draws a line
Of the three, time shows the difference most readily. Laboratory roasting is counted in seconds, hiire in minutes or hours. But a 1999 study and an industry body's account both describe roasting of more than ten minutes (Figure 5-4-1, in “Tea roasting temperature: what 180°C, 200°C and 220°C actually measured”), so time alone cannot draw the line. The other two, purpose and evaluation, cannot be compared head-on, because the stages differ — but that difference of stage was itself the line. Hiire meets aracha, not yet finished. The roasting fire meets sencha and bancha already fired. The same fire aroma is deducted at the earlier stage and sold at the later one. The packet writes it as "light roast" and "dark roast". Whether there is a shared standard behind those words is for the next chapter.