coffee roasting
process / process-coffee-roasting
コーヒー焙煎
Roasting coffee beans. Differences in the temporal dominance of taste and aroma by roast level are treated separately.
Photographs (captions in Japanese)
ウガンダでのコーヒー豆焙煎の実施場面。焙煎という工程が実際に行われている様子を示す写真。
写っているもの: Coffea（コーヒー豆）の焙煎工程部位・状態: 焙煎作業中の場面
写真: Erinamukuta／ CC BY-SA 4.0／ 原画像／ 台帳の原画像
写真の範囲と来歴
被写体の確認: 原典の記載による同定。
掲載画像: Wikimedia Commons の原寸ファイルを sips で長辺2400pxに縮小。苦味研究所では切り抜き・色調変更なし（リサイズのみ）。 表示用には幅1200px上限のWebPを配信し、台帳の原画像は上のリンクから確認できます。
On this page (10 sections)
Reading the bitterness
A study of medium- and dark-roasted Arabica coffee using TDS (temporal dominance of sensations) and intranasal PTR-ToF-MS measurements showed that the temporal pattern of dominant flavors during drinking differs by roast level. Bitterness and roasted aroma dominated periods of the medium roast, whereas bitterness and burnt aroma dominated the dark roast. Only 1 level of roasting conditions was examined for each, however, and the 『優勢率』 (“dominance rate”) shown by TDS is not a measure of sensory intensity itself.
An analysis of Arabica green beans from Doi Chaang in Chiang Rai Province, Thailand (honey process; cup score above 80) found that total phenolic and chlorogenic acid content decreased significantly as roasting increased from light to medium to dark, whereas caffeic acid, a breakdown product, increased. The lightness (L* value) of roasted beans correlated, according to the study, positively with chlorogenic acid content and negatively with caffeic acid content. The study was limited to 1 lot from a single farm and did not include human sensory evaluation.
A report analyzing volatile compounds in the same Doi Chaang Arabica by HS-SPME-GC/MS discusses changes in furfuryl alcohol content with roast level in connection with a description in other literature of 『焦げた・ロースト香が苦味として知覚される』 (“burnt and roasted aromas being perceived as bitterness”) arising through the Maillard reaction. This link appears in the discussion; the study itself did not measure bitterness in people.
Sources for this overview
Effects of Roasting Level and Milk Addition on In Vivo Aroma Release and Perception of Coffee
Checked for this overview: Confirmed through TDS the dominant pattern of bitterness, roasted aroma, and burnt aroma for medium and dark roasts.
Checked for this overview: Confirmed decreases in total phenolics and chlorogenic acid and an increase in caffeic acid as roast level rose. / Confirmed the discussion’s description of changes in furfuryl alcohol and 『苦味として知覚される』 (“perceived as bitterness”).
Follow the connections
coffee roasting →can change→ chlorogenic acid
coffee roasting →is associated with→ bitterness →can be measured separately …→ astringency
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 (3)
Scope: Comparison of Temporal Dominance of Sensations (TDS) between medium-roast and dark-roast Arabica
Note: For medium roast, bitterness and roasty aroma dominate; for dark roast, bitterness and burnt aroma dominate. TDS is not an intensity curve.
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process-coffee-roasting —can_change→ "The temporal composition of bitterness, roasty aroma, and burnt aroma that dominate during drinking"Scope: Volatile compound analysis of Doi Chang-grown arabica (HS-SPME-GC/MS, comparing light, medium, and dark roasts)
Note: The body of the paper connects the change in furfuryl alcohol content with roast level to a description, via the Maillard reaction, that 「焦げた・ロースト香が苦味として知覚される(perceived as a bitter taste)」. However, this description is a discussion grounded in other literature, not the study's own human sensory measurement, so it is treated as contextual.
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process-coffee-roasting —is_associated_with→ sensation-bitterScope: Ethiopian arabica beans; comparison of ultra-high-pressure-processed cold brew and conventional cold brew
Note: As roast degree deepened from Agtron color value 73 (light) → 62 (medium) → 53 (dark), the bitterness score increased significantly (ultra-high-pressure: 2.00±0.10 → 3.35±0.30 → 5.50±0.40; conventional: 3.00±0.28 → 4.30±0.42 → 6.50±0.42; p<0.05 in both). This is an academic source that directly shows, with statistical significance from a human sensory panel, the relationship that deeper roasting means stronger bitterness. The same directional trend was confirmed regardless of extraction method (both of the 2 extraction conditions: ultra-high-pressure and conventional).
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process-coffee-roasting —can_change→ "Sensory bitterness score (rated out of 10 by 12 trained assessors holding Q Arabica Grader certification)"Mechanism and receptors (1)
Scope: Chapter 7 (the chemistry of coffee's taste) of the SCA's official Coffee Sensory and Cupping Handbook (2021)
Note: Original text: "Sourness is preponderant in light roasts and bitterness in dark roasts." "bitterness actually increases with the roast level". It explicitly states that caffeine is only one part of coffee's bitterness compounds, and that bitterness increases even though caffeine decreases with roasting ("caffeine ... only accounts for a small percentage of coffee's bitterness").
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process-coffee-roasting —increases→ sensation-bitterHow processing and cooking change it (1)
Scope: Comparison of light roast (180°C), medium roast (200-220°C), and dark roast (230°C); total phenolic content quantified by the Folin-Ciocalteu method, and chlorogenic acid and caffeic acid quantified by UPLC
Note: The lightness L* value correlated positively with chlorogenic acid content (r=+0.9101) and negatively with caffeic acid content (r=-0.9360). This is a single lot (n=1) from a single farm, and no human sensory panel was conducted.
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process-coffee-roasting —can_change→ compound-chlorogenic-acidSafety and regulation (2)
Scope: Product description on the SCA's official store
Note: The SCA's own official description of a visual reference tool it distributes. The accompanying manual is authored by Carl Staub. It is positioned not as an academic definition of roast level but as an industry consensus-building tool for roasters and customers to reach a shared understanding of roast level.
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process-coffee-roasting —is_classified_by→ "The "Agtron Roast Color Kit" officially distributed by the SCA (Specialty Coffee Association). It consists of 8 color disks housed in a white vinyl case, numbered in 10% increments from "Very Light" (tile #95) to "Very Dark" (tile #25)."Scope: At the time of the UC Davis Coffee Center research announcement and the trade-press report on the SCA white paper.
Note: This research is at the proposal stage toward standardization, not an established new standard. The materials checked here did not state the procedure or timing for developing it. They also did not specify how existing Agtron 8-level classifications or terms such as French and Italian would be treated (separated into a research question in leads).
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process-coffee-roasting —is_classified_by→ "According to trade-press reporting, SCA may use a 「universal roasted arabica coffee color curve(普遍的な焙煎アラビカコーヒーの色曲線)」 (“universal roasted arabica coffee color curve”) identified by UC Davis Coffee Center research (7 roast profiles × 3 origins = washed Ugandan, washed Indonesian, and honey-process Central American; 663 samples and 39 experimental roasts; measured in L*a*b* color space) to develop a roast-color standard based on visible-light measurement. The trade publication reports that SCA published a white paper in that direction and is developing a draft."Culture (5)
Scope: A column article on the All Japan Coffee Association's official website
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process-coffee-roasting —has_standardized_vocabulary_entry_in→ "The 8-stage roast-level terminology listed in the 「知る・楽しむ」 (in translation: "Learn and Enjoy") section of the All Japan Coffee Association's official website — light roast, cinnamon roast, medium roast, high roast, city roast, full city roast, French roast, and Italian roast."Scope: An article on the official SCA site (by Peter Giuliano) introducing Ukers’s (1928) description.
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process-coffee-roasting —has_term_first_appearing_in→ "The 8 terms for roast level, 「light・cinnamon・medium・high・city・full city・French・Italian」 (light, cinnamon, medium, high, city, full city, French, and Italian), are described as recorded in William Ukers's book 『All About Coffee』 (1928)."Scope: Concerns raised about roast-level terminology by the SCA, people connected with the UC Davis Coffee Center, and trade publications
Note: A peer-reviewed journal article (Anokye-Bempah et al. 2025) and multiple SCA official articles and trade-press articles independently raise the same concern. This fact calls into question the very premise that 「地域名のついた焙煎度呼称が実際にその地域の慣行を一意に指す」 (in translation: "a roast-level term carrying a regional name actually refers uniquely to that region's practice").
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process-coffee-roasting —has_unresolved_property→ "There is no universally agreed standard in the roasting industry for what "light roast," "medium roast," and "dark roast" mean; one roaster's "light roast" can even be darker than another roaster's "dark roast." The SCA itself states that terms carrying regional names, such as French, Italian, and Full City, can be "too arcane or flexible to be meaningful.""Scope: Pendergrast, 『Uncommon Grounds』, chapter "The European Coffee Scene", on Europe in the 1920s–30s.
Note: This is a cited general book on coffee history, not a peer-reviewed academic paper. The page number in the original book has not been checked (the passage was verified through a site reproducing the full text). This passage alone cannot establish whether today’s retail terms 「イタリアン・ロースト」「フレンチ・ロースト」 (“Italian roast” and “French roast”) descend directly from those historical regional practices (separated into a research question in leads).
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process-coffee-roasting —is_presented_as→ "Coffee historian Mark Pendergrast’s book 『Uncommon Grounds』 (1999) states of Europe in the past: 「フランス人・イタリア人・ポルトガル人・スペイン人は、アラビカに加えるようになったロブスタ特有の苦味を隠す、より深い焙煎を好んだ」 (“The French, Italians, Portuguese, and Spanish enjoyed darker roasts that hid some of the bitter-tasting robustas they now added to the arabica beans”). It also notes a north–south difference within Italy: 「南に行くほど焙煎は深くなる傾向があり、南部イタリア人はほとんど豆を炭化させる一方、北部イタリア人は中程度の焙煎を好んだ」 (“The farther south, the darker the roast tended to be, so that southern Italians nearly turned their beans to charcoal, while northern Italians enjoyed a moderate roast”)."Scope: Interviews (2023) with specialty coffee roasters in Norway and Denmark
Note: A 2023 interview article from the trade publication Perfect Daily Grind. Note that while the roasting style itself carrying the regional name "Nordic" traces back to specific roasters and a specific period, the person who established the style himself voices disagreement with that very regional-name label. Whether a term carrying a regional name uniquely refers to that region's practice is not generalized here.
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process-coffee-roasting —has_historical_origin→ "The so-called "Nordic light roast" style traces back to specific, named individual roasters — Tim Wendelboe, who opened a roastery in Oslo, and Klaus Thomsen, co-founder of Copenhagen's Coffee Collective, among them. Wendelboe recounts that the turning point was noticing that his own roasted beans tasted burnt compared with the coffee samples brought in by exporters. Thomsen himself, while saying he does not like the term "Nordic roasting," acknowledges that this approach itself — roasting as light as possible and holding back coffee's inherent development — carries major worldwide influence."