charcoal roasting
process / process-charcoal-roasting
炭火焙煎
Roasting or heating with charcoal as the heat source, used in coffee and in finishing some teas.
On this page (6 sections)
Reading the bitterness
A 2024 study of Chinese large-leaf yellow tea made samples by charcoal, electric, and drum roasting from the same batch of fresh leaves (picked June 20, 2023) and measured taste with an electronic tongue (e-tongue). The bitterness output was significantly higher with charcoal roasting, 3.10±0.12, than with electric roasting, 2.54±0.17, or drum roasting, 2.32±0.23. Astringency output was highest with drum roasting, followed by charcoal and then electric roasting. Contrary to the popular account that charcoal roasting softens bitterness and astringency, this measurement gave charcoal the highest bitterness output among the 3 methods.
A coffee specialty shop's web article, meanwhile, says charcoal roasting 「炭の遠赤外線でじっくりと熱を加える」 (in translation: "applies heat slowly with charcoal's far-infrared radiation"), so that 「豆の芯まで均一に熱が伝わり、独特の香ばしさと深いコクが生まれ」 (in translation: "heat reaches the beans' centers evenly, creating a distinctive roasted aroma and deep body") and 「苦味や酸味がまろやかに調和」 (in translation: "bitterness and acidity harmonize mellowly"). It gives a roast time of 15–20 minutes and temperature of about 200–250 degrees, but provides no measured data or sources and names no individual author.
Another view exists within the industry. Based on exchanges with roasters, a cafe owner and barista writes from experience that charcoal aroma is strong enough to cancel other aromas, obscuring each bean's character. With charcoal as the heat source in hot-air roasting, charcoal aroma is less likely to cling to beans; in a direct-fire roaster with an air passage underneath, charcoal aroma enters the roaster and transfers to them, the writer says. This runs counter to the account of mellowing and shows that industry views of charcoal roasting differ.
Sources for this overview
Checked for this overview: Used the measurement giving charcoal the highest bitterness output as evidence for this paragraph.
Checked for this overview: Used the industry account of softened bitterness as evidence for this paragraph.
Checked for this overview: Used the opposite assessment of overly strong aroma as evidence for this paragraph.
Hypotheses and recipe candidates for this entry are on the Japanese page.
Structured claims — open a section to read each claim's confidence, evidence and limits
Sensory (1)
Scope: Chinese large-leaf yellow tea; a comparison of 3 roasting methods from a single fresh-leaf batch.
Note: The e-tongue output values are a dimensionless sensor response and are not generalized to human sensory evaluation or to Japanese green tea/hojicha. Contrary to the popular narrative that charcoal roasting mellows bitterness and astringency, it is noteworthy that in this e-tongue measurement, charcoal roasting showed the highest bitterness output value among the 3 methods.
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process-charcoal-roasting —has_sensory_response→ "Large-leaf yellow tea made from the same fresh-leaf batch (picked June 20, 2023) was processed under charcoal roasting (CR: roasting-basket surface temperature 145±5°C, leaf temperature 125±10°C), electric roasting (ER: dryer temperature 145°C, leaf temperature 125±5°C), and drum roasting (DR: drum inner-wall temperature 145°C, leaf temperature 90±5°C), all for 95 minutes or more, and taste was measured with an electronic tongue (e-tongue). The bitterness output values were CR 3.10±0.12, ER 2.54±0.17, and DR 2.32±0.23, with CR significantly higher than the other 2 methods (at the p=0.05 level, only CR carried a different statistical letter from the others). The astringency output values were highest for DR at 13.07±0.24, followed by CR at 10.43±0.06 and ER at 9.61±0.14, with significant differences between every pair."Culture (2)
Scope: General industry discourse on charcoal roasting coffee.
Note: Presented as an experiential explanation without measured data or analysis. No individual author is named.
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process-charcoal-roasting —is_presented_as→ "A coffee specialty shop's web article says charcoal roasting 「炭の遠赤外線でじっくりと熱を加える」 (in translation: "applies heat slowly with charcoal's far-infrared radiation"), so 「豆の芯まで均一に熱が伝わり、独特の香ばしさと深いコクが生まれ」 (in translation: "heat reaches the beans' centers evenly, creating a distinctive roasted aroma and deep body") and 「苦味や酸味がまろやかに調和」 (in translation: "bitterness and acidity harmonize mellowly"). It also gives a roast time of 15–20 minutes and about 200–250 degrees, but cites no sources."Scope: One barista's view of charcoal roasting coffee.
Note: An account based on the author's experience and industry exchanges, without measured data. Unlike the 「まろやかになる」 (in translation: "becomes mellow") account, it gives the opposite assessment that charcoal aroma can be so strong it obscures the beans' character, showing that industry accounts differ.
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process-charcoal-roasting —is_presented_as→ "Based on experience and exchanges with roasters, an article by a cafe owner and barista says 「炭の香りは他の香りを打ち消すほど強い香りの部類に入る」 (in translation: "charcoal aroma is strong enough to cancel out other aromas"), making bean characteristics harder to discern and differences between beans harder to enjoy. It explains that charcoal aroma transfers less readily when charcoal fuels hot-air roasting, but in a direct-fire roaster with an air passage underneath, charcoal aroma enters the roaster and transfers to the beans."