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.
Show data
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.
Show data
process-hojicha-roasting —has_composition→ "Total amino acid content (mg per 100 ml of tea liquor) decreased sharply with roasting: for first-flush tea, aracha 33.52 → light roast 4.10 → medium roast 3.90 → dark roast 3.10; for karibancha, 15.32 → 2.77 → 2.38 → 2.32; for second-flush tea, 4.10 → 2.87 → 2.74 → 1.97. The aracha contained 11 kinds of amino acids for first-flush tea and karibancha, and 8 kinds for second-flush tea; in the light-roast first-flush tea, 8 kinds remained, including theanine, aspartic acid, glutamic acid, and arginine, while in the medium- and dark-roast karibancha and second-flush tea, only 3 kinds remained — γ-aminobutyric acid, glutamic acid, and serine. Among these, γ-aminobutyric acid accounted for about 70% of the total amino acids."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→ "A medium-roast sample of Ooishida-kuki stem tea from Suizawa, Mie Prefecture, roasted at 150°C for 12 minutes, was described in the paper's aroma evaluation as "Bitter aroma, burnt roasted aroma." The same raw material roasted at 130°C for 10 minutes as a light-roast sample was described as "Preferable roasted aroma," and the unroasted aracha was "Fresh greenish, toasted laver-like.""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→ "2-ethyl-3,5-dimethylpyrazine and tetramethylpyrazine, aroma compounds of roast fragrance, were not detected in aracha but were detected after roasting (except for tetramethylpyrazine in second-flush tea). By roast level, the amounts of both compounds were higher the lighter the roast for first-flush tea and karibancha, while second-flush tea showed no difference by roast level. By tea flush, first-flush tea had the most, followed by karibancha, with second-flush tea the least."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→ "Using a Morita-type automatic continuous hojicha roasting machine (2 kg input), a total of 14 kinds of aracha (unrefined tea) and their infusions — open-field-grown sencha, shade-grown (kabuse) sencha, tamaryokucha, and others from Shizuoka, Mie, and Saga — were roasted as samples under each of the following conditions: a strong roast at 100°C for 15 minutes, a light roast at 130°C for 10 minutes, and a deep roast at 150°C for 12 minutes. The raw aracha (Oshita stem tea, kabuse stem tea) from Suizawa-en in Mie Prefecture had already been through a firing step (80°C for 20 minutes). GC/MS analysis newly identified 86 compounds in hojicha and 44 compounds in kamairi-cha (pan-fired tea), compared with green tea."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.
Show data
process-hojicha-roasting —can_generate→ "In both hojicha and pan-fired tea, Maillard products of sugars and amino acids, including pyrazines, pyrroles, furans, and pyranones, made up the main portion of aroma compounds. In particular, 1-ethyl-3,4-dehydropyrrolidone, described as a heated reaction product of L-theanine and sugars, was detected at the highest concentration in both roasted and pan-fired tea."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.
Show data
process-hojicha-roasting —reduces→ compound-egcgShow data
process-hojicha-roasting —can_generate→ "Non-epi gallocatechin gallate (mg per 100 ml of tea liquor) was higher after roasting than in crude tea: first-flush tea 0.46 → 5.23 light → 3.53 medium → 1.38 dark; karibancha 0.32 → 2.81 → 2.07 → 0.42; second-flush tea 0.83 → 8.21 → 5.88 → 2.41. In some harvest periods, catechin gallate and gallocatechin likewise had higher values after roasting than in crude tea."