Descriptions of hojicha say how strong the fire is. "Over a strong fire." "High heat, all at once." Not many carry a number. The numbers are in the research, and a 2020 report in which a prefectural institute and a university in Ishikawa roasted bōcha holds three: 180°C, 200°C and 220°C.

What did those three temperatures establish?

That within that range, the higher the temperature the more the toasty aroma compounds increase, and the colour moves from yellow-green towards yellow-red. What they did not establish is what temperature the leaf itself reached.

The 180°C was the inner surface of the drum

Which leaves the question of what the 180°C is a temperature of. In this report it is the inner surface of the drum, measured with an infrared thermometer. It is not the temperature of the leaf. Other reports measured in other places, and some documents do not say at all (Figure 5-4-1).

Figure 5-4-1Roasting and hiire temperatures are measured in different places from source to source

Source (year)TemperatureWhat the temperature was measured onTime
Shiono 1974, tray type65°Cexhaust temperature5 hours
Japan Tea Central Association, Green tea labelling standard, appendixhiire 70–130°C / roasting 140°C or abovenot statednot stated
Shiono 1974, air-through type90–110°Cinternal temperature20–25 minutes
Takahashi 2015around 100°C (80°C for higher grades)not stated30–40 minutes
Kochi Prefecture (Table 1, 2013)exhaust temperature 100°C at the second roasting (the same for light, medium and dark)exhaust temperaturenot stated
NARO 2015100 / 115 / 130°Cleaf surface temperaturenot stated
Kawakami 1999150 / 130 / 100°Cnot stated12 min / 10 min / 15 min
Shiono 1974, drum-over-fire type140–150°Cexhaust temperature40–60 minutes
Hara 1970160–180°Cdrum inner wall temperaturenot stated
Sasaki et al. 2020180 / 200 / 220°Cdrum inner surface temperature (infrared thermometer)40–420 seconds
GJTA (an industry body)200°Cnot stated10 minutes or more
Temperature, place of measurement and time for roasting and for hiire, source by source, from the lower temperatures to the higher. "Not stated" means the source does not say; nothing has been estimated to fill it. The time column carries only the values written in the sources, with no conversions. The labelling standard row is not a definition of tea types but a worked list for sorting out who is responsible for the labelling. The Kochi Prefecture row has no time; the report records only exhaust temperature and rotation speed (first-flush tea was separated by drum speeds of 17 / 12 / 8 rpm; the first roasting was at an exhaust temperature of 90°C and 22 rpm). GJTA (Global Japanese Tea Association) is an industry body's account. Sources: Shiono T. (1974); Takahashi J. (2015); Tea Research Station, Kochi Prefectural Agricultural Technology Center (data for 2013); NARO National Institute of Vegetable and Tea Science (2015); Hara T. and Kubota E. (1970); Kawakami M. and Yamanishi T. (1999); Sasaki et al. (2020); Japan Tea Central Association, Green tea labelling standard (last amended 2026); GJTA.