hojicha roasting
process / process-hojicha-roasting
ほうじ茶の焙煎
Roasting green tea to make hojicha. Roast level, such as light, medium, or dark, depends on exhaust temperature, drum rotation speed, and time.
On this page (8 sections)
Reading the bitterness
Hojicha roasting heats crude green tea at levels such as light, medium, and dark. In a trial at the Kochi Prefectural Agricultural Technology Center Tea Experiment Station, first-flush, karibancha, and second-flush crude teas steamed for 50 seconds were roasted in an automatic continuous hojicha roaster. Total catechins (per 100 ml of tea liquor) fell with increasing roast level: first-flush tea from 34.89 mg in crude tea to 21.86 mg light, 14.59 mg medium, and 6.98 mg dark; karibancha from 25.31 mg to 2.33 mg; and second-flush tea from 54.51 mg to 8.68 mg. Non-epi catechins such as gallocatechin gallate, however, showed a hump-shaped pattern, first increasing from crude tea to light roast and then decreasing with deeper roasting.
Epigallocatechin gallate (EGCG) and epicatechin gallate (ECG), gallated catechins recorded by NIGAMI LAB as activating the bitter receptor TAS2R39, also fell markedly as roasting deepened. EGCG (per 100 ml of tea liquor) in first-flush tea fell from 20.38 mg in crude tea to 6.29 mg light, 3.15 mg medium, and 1.18 mg dark; in karibancha it fell from 12.82 mg to 0.00 mg at dark roast. The Kochi source measures component amounts only; it did not investigate how these decreases relate to sensory ratings of bitterness. Caffeine hardly decreased under light roasting (101% of crude tea in first-flush tea), whereas under dark roasting it decreased by 6–13%, to 94% in first-flush tea and 87% in karibancha.
Total amino acids also drop sharply on roasting. In the same Kochi trial, total amino acids in first-flush tea (per 100 ml of tea liquor) fell from 33.52 mg in crude tea to 4.10 mg light, 3.90 mg medium, and 3.10 mg dark. Crude tea had 11 amino acids in first-flush tea and karibancha and 8 in second-flush tea, but only 3—gamma-aminobutyric acid, glutamic acid, and serine—remained in medium- and dark-roasted karibancha and second-flush tea; gamma-aminobutyric acid accounted for about 70% of total amino acids. The report classifies arginine, leucine, lysine, and gamma-aminobutyric acid by their bitter taste, but this is a general taste classification of isolated amino acids, not a sensory measurement of hojicha bitterness itself.
Roasting also generates aroma compounds. In the Kochi trial, roasting-aroma components such as 2-ethyl-3,5-dimethyl Pyrazine were undetected in crude tea but detected after roasting, and were more abundant at lighter roasts in first-flush tea and karibancha. A 1999 paper on tea from Mie Prefecture found that Maillard products of sugars and amino acids, including pyrazines, pyrroles, furans, and pyranones, dominated the aroma components of both hojicha and pan-fired tea. The highest-concentration compound was 1-ethyl-3,4-dehydropyrrolidone, described as a product of L-theanine and sugars. In that paper, the authors described the aroma of a medium-roasted sample (150°C, 12 minutes) as "Bitter aroma, burnt roasted aroma." This concerns smell, distinct from bitterness perceived as taste in the mouth. A light-roasted sample (130°C, 10 minutes) was described as "Preferable roasted aroma."
Sources for this overview
Checked for this overview: Used as evidence for total catechins by roast level. / Used as evidence for the hump-shaped change in non-epi catechins. / Used as evidence for decreases in EGCG and ECG by roast level. / Used as evidence for caffeine decrease rates by roast level. / Used as evidence for the sharp amino-acid decrease and taste classification. / Used as evidence for the formation pattern of pyrazine aroma compounds.
Checked for this overview: Used as evidence for identification of Maillard reaction products. / Used as evidence for the olfactory description of a bitter aroma.
Follow the connections
hojicha roasting →reduces→ tea catechins →are main contributors to→ astringency
hojicha roasting →reduces→ caffeine →is a poor universal prototy…→ bitterness
hojicha roasting →reduces→ epigallocatechin gallate →is correlated with→ bitterness
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
Composition and content (3)
Scope: Kochi Prefectural Agricultural Technology Center Tea Experiment Station; crude teas of first flush, cut-leaf, and second flush with a 50-second steaming time. Roasted 2 times with an automatic continuous hojicha roaster (exhaust temperature 90 C for the 1st roast, 100 C for the 2nd roast, with drum rotation speed adjusted for each flush and roasting degree).
Note: Direct quantification by HPLC (JASCO X-LC system). Only 1 sample per condition; the number of replicates is not stated.
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process-hojicha-roasting —reduces→ compound-catechinsScope: Kochi Prefectural Agricultural Technology Center, Tea Industry Experiment Station; the same first-flush, karibancha, and second-flush tea samples as above.
Note: The remarks column of the report classifies arginine, leucine, lysine, and γ-aminobutyric acid under the 「苦味」 (in translation: "bitterness") taste category, but this is a general taste classification for individual amino acids, not a measurement of hojicha's own sensory bitterness. The connection to bitterness perception is unconfirmed.
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process-hojicha-roasting —has_composition→ (the claim sentence above)Scope: Kochi Prefectural Agricultural Technology Center Tea Experiment Station, 2014; light-roast and deep-roast hojicha made from crude first-flush and cut-leaf tea (roasted 2 times with an automatic continuous hojicha roaster).
Note: Direct quantification by HPLC (Shimadzu).
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process-hojicha-roasting —reduces→ compound-caffeineSensory (1)
Scope: Ooishida-kuki stem tea from Suizawa, Mie Prefecture; sample descriptions from Table I.
Note: This is an olfactory aroma description (aroma descriptor) by the authors, not a taste evaluation of bitterness as tasted in the mouth. The number of evaluators and the scale are not stated, and the specific aromatic quality that "Bitter aroma" refers to cannot be identified from the text. Its connection to bitterness perception in general is treated cautiously.
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process-hojicha-roasting —has_sensory_attribute→ (the claim sentence above)How processing and cooking change it (5)
Scope: Kochi Prefectural Agricultural Technology Center, Tea Industry Experiment Station; aroma compound analysis by GC-MS (extracted by continuous steam distillation).
Note: Reported by a figure (radar chart); no numerical table or number of replicates is given, and no statistical test is shown.
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process-hojicha-roasting —can_generate→ (the claim sentence above)Scope: 2 kinds of sencha — open-field-grown from Shizuoka Prefecture and shade-grown (kabuse) from Mie Prefecture — and their stem tea, plus open-field and shade-grown kamairi-cha from Saga Prefecture.
Note: Aroma concentrate preparation by the infusion extraction method (brewed method); compound identification by GC-MS (HP5972), matching retention indices and MS spectra against reference standards.
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process-hojicha-roasting —is_prepared_by→ (the claim sentence above)Scope: The 14 green-tea and pan-fired tea samples noted above.
Note: Identified by GC/MS. The proposed formation mechanism (Maillard reaction) also draws on findings from prior studies.
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process-hojicha-roasting —can_generate→ (the claim sentence above)Note: Epigallocatechin gallate and epicatechin gallate are recorded in NIGAMI LAB's existing records as gallate-type catechins that activate the human bitter receptor TAS2R39. However, this Kochi Prefecture source measures only compound levels, and how the decrease in compounds from roasting corresponds to a change in bitterness perception cannot be confirmed from this source.
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process-hojicha-roasting —reduces→ compound-egcgShow data
process-hojicha-roasting —can_generate→ (the claim sentence above)