{ "id": "acids-in-coffee", "url": "https://coffearium.org/entries/acids-in-coffee/", "license": "CC-BY-4.0", "title": "Acids in coffee", "summary": "The acids behind coffee's sourness – which ones the green bean brings, which form or break down during roasting, how acidity is measured, and why the cup's acidity is not the taste of any single acid.", "domain": "roasting", "kind": "Concept", "stage": "roast", "topics": [ "science" ], "topicSections": {}, "lang": "en", "status": "verified", "reviewer": "Coffearium verification pass", "lastVerified": "2026-10-14T00:00:00.000Z", "updated": "2026-10-20T00:00:00.000Z", "added": "2026-10-14T00:00:00.000Z", "brief": [ "Acids are responsible for coffee's sourness. Citric, malic, chlorogenic and quinic acids are the main acids in green coffee.1,3", "Roasting reduces citric, malic and chlorogenic acids and forms formic, acetic, glycolic and lactic acids, mainly from sucrose.1", "In a 5 kg drum roaster, titratable acidity peaked during first crack and had fallen back to its starting value by second crack.4", "Titratable acidity is reported as a better predictor of sourness than pH; a study of nine brewing methods found neither correlated with perceived acidity.4,9", "The Specialty Coffee Association (SCA) defines acidity in cupping as “the perception of sour taste provoked by the brew”, rated for intensity and for quality.14,16" ], "quickFacts": [ { "label": "Main acids, green coffee", "value": "Citric, malic, chlorogenic, quinic" }, { "label": "Formed in roasting", "value": "Formic, acetic, glycolic, lactic (mainly from sucrose)" }, { "label": "Brew pH", "value": "4.85–5.15 (arabica); 5.25–5.40 (robusta); one source" }, { "label": "Titratable acidity over a roast", "value": "Peak during first crack; back near the start by second crack (one study)" }, { "label": "Better predictor of sourness", "value": "Titratable acidity rather than pH (contested)" }, { "label": "SCA sour reference", "value": "Citric acid solution, 0.04% (SCA 103-2024) or 0.015% (CVA document)" } ], "aka": [ "Coffee acids", "Organic acids in coffee" ], "linkTerms": [ "coffee acidity", "organic acids", "aliphatic acids", "quinic acid", "citric acid", "malic acid", "formic acid", "glycolic acid", "phosphoric acid" ], "related": [ "roasting", "roast-degree-and-colour", "roast-profile", "development-time", "maillard-reaction", "green-coffee-composition", "cupping", "extraction-yield-and-tds", "water-for-coffee", "brew-methods", "chlorogenic-acids", "water-minerals-and-flavour", "hardness-and-alkalinity" ], "contested": [ "pH versus titratable acidity as a predictor of sourness: a 2024 roasting study states that numerous studies found titratable acidity the better predictor4, and a 2021 drip-coffee study reported a strong correlation of titratable acidity with sourness8; a 2013 comparison of nine brewing methods found that neither pH nor titratable acidity correlated with perceived acidity.9", "Acetic and formic acids in dark roasts: a 2000 paper, citing earlier analyses, reports that formic and acetic acids rise up to a medium roast and then fall1; a 2023 conference study found acetic acid increasing systematically with roast degree and formic acid as the only acid without a systematic change.12", "Two species, arabica and robusta: a 2000 paper reports that arabica brews are more acidic (lower pH) than robusta brews1; according to the authors of a meta-analysis, arabica tends to have lower amounts of organic acids.13 A roasting chemistry chapter states that robusta green coffee contains significantly more chlorogenic acids3, while the meta-analysis found the difference not statistically significant over a much larger sample.13", "Strength of the SCA sour reference: SCA Standard 103-2024 gives a 0.04% citric acid solution14; the SCA's CVA document (June 2024), written for use while the assessments moved through the SCA's standards process, gives 0.015%.15" ], "corrections": [ { "date": "2026-10-20T00:00:00.000Z", "change": "A 2021 conference e-poster on titratable acidity and sourness was removed as a source; its statements now rest on the author's SCA article.", "reason": "Conference posters are not accepted as sources (editorial ruling, 20 Oct 2026)." }, { "date": "2026-10-17T00:00:00.000Z", "change": "The titratable acidity values at second crack are now marked as coming from the African washed coffee only.", "reason": "Cross-check during verification of the new second-crack entry; in Anokye-Bempah et al. 2024 these three profiles used one African washed coffee." } ], "sources": [ { "id": "s1", "title": "Formation of aliphatic acids by carbohydrate degradation during roasting of coffee", "authors": "Ginz, M.; Balzer, H. H.; Bradbury, A. G. W.; Maier, H. G.", "year": 2000, "publisher": "European Food Research and Technology 211(6), 404–410", "url": "https://doi.org/10.1007/s002170000215", "doi": "10.1007/s002170000215", "tier": "A", "quote": "A major fraction of the acidity generated on coffee roasting can be attributed to formation of the four aliphatic acids formic, acetic, glycolic and lactic.", "accessed": "2026-10-14T00:00:00.000Z" }, { "id": "s2", "title": "The Roast – Creating the Beans' Signature", "authors": "Schenker, S.; Rothgeb, T.", "year": 2017, "publisher": "In: Folmer, B. (ed.), The Craft and Science of Coffee, Academic Press, ch. 11, pp. 245–271", "url": "https://doi.org/10.1016/B978-0-12-803520-7.00011-6", "doi": "10.1016/B978-0-12-803520-7.00011-6", "tier": "B", "quote": "As a rule of thumb, increasing degree of roast leads to decreasing acidity and increasing bitterness.", "accessed": "2026-10-14T00:00:00.000Z" }, { "id": "s3", "title": "The Chemistry of Roasting – Decoding Flavor Formation", "authors": "Poisson, L.; Blank, I.; Dunkel, A.; Hofmann, T.", "year": 2017, "publisher": "In: Folmer, B. (ed.), The Craft and Science of Coffee, Academic Press, ch. 12, pp. 273–309", "url": "https://doi.org/10.1016/B978-0-12-803520-7.00012-8", "doi": "10.1016/B978-0-12-803520-7.00012-8", "tier": "B", "quote": "Main nonvolatile acids are CGA, citric, malic, and quinic acid (Maier, 1993).", "accessed": "2026-10-14T00:00:00.000Z" }, { "id": "s4", "title": "The effect of roast profiles on the dynamics of titratable acidity during coffee roasting", "authors": "Anokye-Bempah, L.; Styczynski, T.; de Andrade Teixeira Fernandes, N.; Gervay-Hague, J.; Ristenpart, W. D.; Donis-González, I. R.", "year": 2024, "publisher": "Scientific Reports 14, 8237", "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC11002029/", "doi": "10.1038/s41598-024-57256-y", "tier": "A", "quote": "Here we investigate roast profiles of the same total duration but very different dynamics inside a 5-kg commercial drum roaster, and we show that the TA invariably peaks during first crack and then decays to its original value by second crack.", "accessed": "2026-10-14T00:00:00.000Z" }, { "id": "s5", "title": "The Effect of Roast Development Time Modulations on the Sensory Profile and Chemical Composition of the Coffee Brew as Measured by NMR and DHS-GC–MS", "authors": "Alstrup, J.; Petersen, M. A.; Larsen, F. H.; Münchow, M.", "year": 2020, "publisher": "Beverages 6(4), 70", "url": "https://www.mdpi.com/2306-5710/6/4/70", "doi": "10.3390/beverages6040070", "tier": "A", "quote": "The identified acids showed a general decline in concentration with a prolonged development time.", "accessed": "2026-10-14T00:00:00.000Z" }, { "id": "s6", "title": "Role of Roasting Conditions in the Level of Chlorogenic Acid Content in Coffee Beans: Correlation with Coffee Acidity", "authors": "Moon, J.-K.; Yoo, H. S.; Shibamoto, T.", "year": 2009, "publisher": "Journal of Agricultural and Food Chemistry 57(12), 5365–5369", "url": "https://agris.fao.org/search/en/records/65deb17a6eef00c2cea0ed9f", "doi": "10.1021/jf900012b", "tier": "A", "quote": "A general correlation between total caffeoylquinic acids and pH was observed.", "abstractOnly": true, "accessed": "2026-10-14T00:00:00.000Z" }, { "id": "s7", "title": "Roasting Conditions and Coffee Flavor: A Multi-Study Empirical Investigation", "authors": "Münchow, M.; Alstrup, J.; Steen, I.; Giacalone, D.", "year": 2020, "publisher": "Beverages 6(2), 29", "url": "https://www.mdpi.com/2306-5710/6/2/29", "doi": "10.3390/beverages6020029", "tier": "A", "quote": "With respect to the direction of the correlations, colour (i.e., a darker roast) was positively correlated with bitterness and negatively correlated with sweetness, acidity, and fruitiness (Table 4).", "accessed": "2026-10-14T00:00:00.000Z" }, { "id": "s8", "title": "Manipulating and Measuring a Key Attribute in Drip Brew Coffee", "authors": "Batali, M.", "publisher": "Specialty Coffee Association, 25 Magazine, Issue 15", "url": "https://sca.coffee/sca-news/25/issue-15/manipulating-and-measuring-a-key-attribute-in-drip-brew-coffee", "tier": "B", "quote": "Titratable acidity is shown to strongly correlate to perceived sourness in the descriptive analysis studies.", "accessed": "2026-10-14T00:00:00.000Z" }, { "id": "s9", "title": "Comparison of nine common coffee extraction methods: instrumental and sensory analysis", "authors": "Gloess, A. N.; Schönbächler, B.; Klopprogge, B.; D’Ambrosio, L.; Chatelain, K.; Bongartz, A.; Strittmatter, A.; Rast, M.; Yeretzian, C.", "year": 2013, "publisher": "European Food Research and Technology 236, 607–627", "url": "https://digitalcollection.zhaw.ch/bitstream/11475/4251/2/2013_Gloess-etal_Comparison-of-nine-common-coffee-extraction-methods.pdf", "doi": "10.1007/s00217-013-1917-x", "tier": "A", "quote": "In this study, no correlation between pH or titratable acidity and perceived acidity in flavor or aftersensation was found.", "accessed": "2026-10-14T00:00:00.000Z" }, { "id": "s10", "title": "Acidity and Antioxidant Activity of Cold Brew Coffee", "authors": "Rao, N. Z.; Fuller, M.", "year": 2018, "publisher": "Scientific Reports 8, 16030", "url": "https://www.nature.com/articles/s41598-018-34392-w", "doi": "10.1038/s41598-018-34392-w", "tier": "A", "quote": "All cold brew coffee samples analyzed in this study were found to have lower titratable acid levels", "accessed": "2026-10-21T00:00:00.000Z" }, { "id": "s11", "title": "Water for Extraction – Composition, Recommendations, and Treatment", "authors": "Wellinger, M.; Smrke, S.; Yeretzian, C.", "year": 2017, "publisher": "In: Folmer, B. (ed.), The Craft and Science of Coffee, Academic Press, ch. 16, pp. 381–398", "url": "https://doi.org/10.1016/B978-0-12-803520-7.00016-5", "doi": "10.1016/B978-0-12-803520-7.00016-5", "tier": "B", "quote": "Because alkalinity of water reacts with the extracted acids from coffee, it effectively neutralizes part of the acids.", "accessed": "2026-10-14T00:00:00.000Z" }, { "id": "s12", "title": "Acids in Brewed Coffee: Chemical Composition and Sensory Threshold", "authors": "Birke Rune, C. J.; Giacalone, D.; Steen, I.; Münchow, M.; Duelund, L.; Clausen, M. P.", "year": 2023, "publisher": "SSRN (abstract of a presentation at the 15th Pangborn Sensory Science Symposium, 2023)", "url": "https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4550010", "tier": "B", "quote": "Combined, the results question the direct relation between individual organic acids and acidity in coffee and point towards a more complex understanding of perceived acidity.", "abstractOnly": true, "accessed": "2026-10-14T00:00:00.000Z" }, { "id": "s13", "title": "Acids in Coffee: A Review of Sensory Measurements and Meta-Analysis of Chemical Composition", "authors": "Yeager, S. E.; Batali, M. E.; Guinard, J.-X.; Ristenpart, W. D.", "year": 2021, "publisher": "Specialty Coffee Association, SCA News (summary of the authors' review in Critical Reviews in Food Science and Nutrition)", "url": "https://sca.coffee/sca-news/2021/10/19/acids-in-coffee-a-review-of-sensory-measurements-and-meta-analysis-of-chemical-composition", "tier": "B", "quote": "Arabica coffee tends to have lower amounts of OAs, minimizing at a medium roast level.", "accessed": "2026-10-14T00:00:00.000Z" }, { "id": "s14", "title": "SCA Standard 103-2024 Coffee Value Assessment: Descriptive Assessment", "authors": "Specialty Coffee Association", "year": 2024, "publisher": "Specialty Coffee Association", "url": "https://sca.coffee/s/AW_SCA-103_Descriptive-Assessment_Sept2024_Secured.pdf", "tier": "A", "quote": "Acidity. The perception of sour taste provoked by the brew, which may vary in intensity and character.", "accessed": "2026-10-14T00:00:00.000Z" }, { "id": "s15", "title": "A System to Assess Coffee Value: Understanding the Specialty Coffee Association’s Coffee Value Assessment (June 2024)", "authors": "Specialty Coffee Association (writing team Fernández-Alduenda, M.; Ionescu, K. E.; Giuliano, P.; Rugolo, J.; Delrue, R.)", "year": 2024, "publisher": "Specialty Coffee Association", "url": "https://static1.squarespace.com/static/584f6bbef5e23149e5522201/t/667182ffdde8a5081afc2d8c/1718715138872/SCA+-+A+System+to+Asssess+Coffee+Value+-+June+2024+(Secured).pdf", "tier": "A/B", "tierNote": "A for its definitions and taste references (section 6); B for its explanations of acidity descriptors.", "quote": "Unfortunately, we have no sensory references for terms such as “juicy acidity” or “bright acidity,” and the use of organic acids as references tends to be misleading, as coffees often have a mixture of many different organic acids.", "accessed": "2026-10-14T00:00:00.000Z" }, { "id": "s16", "title": "SCA Standard 104-2024 Coffee Value Assessment: Affective Assessment", "authors": "Specialty Coffee Association", "year": 2024, "publisher": "Specialty Coffee Association", "url": "https://sca.coffee/s/AW_SCA-104_Affective-Assessment_Sept2024_Secured.pdf", "tier": "A", "quote": "Acidity. The perception of sour taste provoked by the brew, which may vary in intensity and character.", "accessed": "2026-10-14T00:00:00.000Z" }, { "id": "s17", "title": "The Brew – Extracting for Excellence", "authors": "Mestdagh, F.; Glabasnia, A.; Giuliano, P.", "year": 2017, "publisher": "In: Folmer, B. (ed.), The Craft and Science of Coffee, Academic Press, ch. 15, pp. 355–380", "url": "https://doi.org/10.1016/B978-0-12-803520-7.00015-3", "doi": "10.1016/B978-0-12-803520-7.00015-3", "tier": "B", "quote": "Highly soluble compounds like sugars or acids are proportionally more abundant turning the flavor profile toward sweet/acidic notes.", "accessed": "2026-10-14T00:00:00.000Z" } ], "markdown": "## What makes coffee acidic\n\nAcids are responsible for sourness. Together with aroma and bitterness, sourness is a key part of how a coffee tastes.1 The main acids in green coffee are citric, malic, chlorogenic and quinic acid.1,3 Roasting removes some of them and forms new ones.1\n\nAccording to the lead author of a drip-coffee study, writing for the Specialty Coffee Association (SCA), coffee's acids are weak acids. They release only part of their hydrogen ions in solution, yet still trigger the sour receptors on the tongue.8\n\nTwo measures are in use:\n\n- **pH** reflects the concentration of free hydrogen ions in the brew at that moment.8\n- **Titratable acidity** is the amount of base, usually sodium hydroxide, needed to bring a set volume of brew to a set pH.4,8\n\nA 2000 paper reports that arabica brews are more acidic than robusta brews: pH 4.85–5.15 against 5.25–5.40.1 Two brews can share a pH and still differ in titratable acidity.10 In a 2018 study of light roasts, hot and cold brews had comparable pH, 4.85–5.13, but the hot brews held more titratable acid.10\n\n## Where the acids come from\n\nRoasting changes the acid profile in three ways. The acids of the green bean break down, chlorogenic acids split, and sugars form new acids.1\n\n
\n
\n
    \n
  1. Citric acid. Present in green coffee; it decreases during roasting.1,2
    2. \n
  2. Malic acid. Also from the green bean; it decreases in the same way.1,2
    3. \n
  3. Chlorogenic acids. Strongly degraded.2 In one study, about half was left after 12 min at 230 °C and almost none after 21 min at 250 °C.6
    4. \n
  4. Quinic acid. Released as chlorogenic acids break down; it increases.1
    5. \n
  5. Formic and acetic acids. Very low in green coffee and formed from sugars.2 They increase up to a medium roast, then fall.1 One 2023 study disagrees (see Contested).12
    6. \n
  6. Glycolic and lactic acids. Also formed from sugars; they keep increasing even in dark roasts.1
    7. \n
\n
How the main acid groups change from green coffee to a dark roast. Band width shows the direction of change, not amounts.1,2,6 Schematic, not to scale.
\n
\n\n**Acids of the green bean.** Citric, malic and chlorogenic acids decrease during roasting, while quinic acid increases.1 Total chlorogenic acids fall with the intensity of roasting.6\n\n**Chlorogenic acids split.** Their breakdown releases quinic acid and phenolic acids; both chlorogenic and quinic acids also form lactones during roasting.1 For that reason, a 2000 paper concludes that chlorogenic acid apparently does not add to the acidity gained in roasting.1 The lactones are bitter, not sour (see Deep dive).2,3\n\n**Sugars form new acids.** Four aliphatic acids – formic, acetic, glycolic and lactic – account for a major part of the acidity formed in roasting.1 Their main precursor in the green bean is sucrose, which makes up 3–8% of green coffee.1\n\nAccording to a 2023 conference study, phosphoric acid also increased with roast degree.12\n\n## How acidity changes during the roast\n\nBecause some acids form while others break down, acidity does not simply fall from the start.1,4 In a 2024 study on a 5 kg drum roaster, beans were sampled every minute of 16-minute roasts.4 The titratable acidity of their brews rose, peaked during first crack, and fell back to its starting value by second crack.4\n\n
\n
\n
Titratable acidity of brews from beans sampled during 16-minute roasts in a 5 kg drum. Values for green coffee, first crack, second crack and the end.4
\n
\n\nThe roast profile changed how fast acidity rose and fell. It barely changed the peak: seven profiles and three coffees peaked at about the same level.4 All roasts in that study ran past second crack.4\n\nThe same pattern appears in pH. A 2000 study roasted robusta for 3 minutes at different temperatures. Extract pH fell from 6.1 at 150 °C to 5.7 at 240 °C, then rose to 6.3 at 280 °C.1 The paper considers the formation of the four aliphatic acids, particularly formic and acetic acids, a key factor in the pH minimum at medium roasts.1\n\nIn the cup, darker roasts taste less acidic. In a 2020 analysis of eight sensory studies, darker roasts went with more bitterness and less acidity, fruitiness and sweetness.7 According to two roasting textbook chapters, light roasts give more acidity in the cup than dark roasts.2,3\n\n## pH, titratable acidity and sourness\n\nA 2024 roasting study states that numerous studies found titratable acidity a better predictor of sourness than pH.4 In a 2021 drip-coffee study, titratable acidity correlated strongly with perceived sourness.8 In one of its experiments pH showed no relation to sourness; in another, only a weak one.8\n\nThe evidence is not uniform. A 2013 comparison of nine brewing methods found no correlation between perceived acidity and either pH or titratable acidity.9 Its brews ranged from filter coffee at about 1% total solids to espressos above 4%.9\n\nStrength matters. In the drip-coffee study, titratable acidity rose in a straight line with total dissolved solids (TDS), the brew's strength.8 It showed little dependence on extraction yield.8 Water also plays a part: its alkalinity neutralises part of the coffee's acids.11\n\n## Acidity in cupping\n\nIn cupping, “acidity” is a sensory attribute, not a chemical measurement. The SCA defines it as “the perception of sour taste provoked by the brew, which may vary in intensity and character”.14,16 In the Coffee Value Assessment (CVA), acidity is rated twice. The descriptive form rates its intensity on a 15-point scale; the affective form rates the impression of its quality on a 9-point scale.14,16\n\nThe SCA's taste reference for sour is a citric acid solution.14,15 According to the SCA, there are no sensory references for terms such as “juicy” or “bright” acidity. Organic acids used as references tend to mislead, because coffees contain a mixture of many acids.15\n\nNaming a coffee's acidity after one acid is therefore unreliable.12,15 According to the SCA, an acidity that reminds a taster of green apple has a good chance of not being malic acid.15 In a 2023 conference study, coffee experts did not correctly identify any of five acids added to coffee at their usual concentrations.12\n\n\n\n## The main acids\n\nThe table lists the main acids, where they come from, how roasting changes them and what is known about their taste. Roasting directions are for the bean or its brew, as stated.\n\n| Acid | Origin | Change in roasting | Sensory note |\n|---|---|---|---|\n| Citric | Green bean1,3 | Decreases1,2,12 | Highly relevant for the acidic taste2,3; the only acid whose detection threshold lay clearly below its concentration in coffee, in one study12 |\n| Malic | Green bean1,3 | Decreases1,2,12 | Highly relevant for the acidic taste2,3; detection threshold around its concentration in coffee12 |\n| Chlorogenic acids (mainly caffeoylquinic acids) | Green bean1,3 | Strongly degraded2,6 | Very limited contribution to sensory perception2; their lactones are bitter2,3 |\n| Quinic | Green bean; released from chlorogenic acids1,3 | Increases1,2,12 | More bitter than sour, according to an SCA article8 |\n| Formic | Formed from sugars1 | Rises to a medium roast, then falls1; no systematic change in one study (see Contested)12 | Strong contributor to perceived acidity2,3 |\n| Acetic | Formed from sugars1 | Rises to a medium roast, then falls1; increased with roast degree in one study (see Contested)12 | Strong contributor to perceived acidity2,3; detection threshold around its concentration in coffee12 |\n| Glycolic | Formed from sugars1 | Keeps increasing into dark roasts1,12 | No sensory data found in the sources opened |\n| Lactic | Formed from sugars1 | Keeps increasing into dark roasts1,12 | Detection threshold around its concentration in coffee12 |\n| Phosphoric | Not stated in the sources opened | Increased with roast degree in one study12 | Detection threshold around its concentration in coffee12 |\n\nThe sensory notes from the 2023 conference study come from an abstract. It reports detection thresholds for citric, malic, acetic, lactic and phosphoric acid in brewed coffee.12 Apart from citric acid, the thresholds lay around the acids' actual concentrations. The authors read this as a contribution to overall acidity, but not one an individual acid can be tasted by.12 Its numbers are not given here, because no second source confirms them.\n\n## How sugars become acids\n\nA 2000 study traced the four aliphatic acids to their precursors. Green robusta beans were soaked in sucrose, glucose or fructose solutions, dried back to their initial moisture of about 10% (basis not stated) and roasted for 3 minutes at 150–280 °C in a sample roaster.1 Sucrose-treated beans gave more than twice the formic and acetic acid of the control, and glycolic acid rose even more; lactic acid did not change significantly.1\n\nModel roasts of the pure sugars mixed with sand (240 °C, 15 min) gave the same four acids, in amounts largely independent of the sugar used.1 Sucrose reacts more slowly at first, because its glycosidic bond must be split before the more reactive reducing sugars appear.1 Labelling with carbon-13 showed how the sugar chain breaks: through endiols and deoxyglucosones into fragments that end as formic, acetic, glycolic and lactic acid.1\n\nSeveral further findings shape what reaches the cup:\n\n- **Intermediates.** Arabinose, erythrose and 1,6-anhydroglucose formed from the sugars and gave the same four acids when roasted themselves.1\n- **Polysaccharides.** Arabinogalactan, a cell-wall polysaccharide, also contributes, with relatively more acetic acid.1\n- **Oxygen.** Roasting sucrose under argon gave similar acid profiles, so oxygen plays no measurable role.1\n- **Amino acids and evaporation.** Glycine lowered the yield of formic acid in model roasts.1 In a real roaster, formic and acetic acids are partly lost by evaporation.1\n\n## Chlorogenic acids, lactones and bitterness\n\nChlorogenic acids are esters of hydroxycinnamic acids, such as caffeic and ferulic acid, with quinic acid.3 Caffeoylquinic acids are the main group, and 5-caffeoylquinic acid (5-CQA) is the most abundant isomer.3 During roasting they break down into quinic acid and hydroxycinnamic acids, or form lactones.1,3\n\nThe losses are large. In a 2009 study, total chlorogenic acids in seven commercial coffees were 34.43–41.64 mg/g green and 2.05–7.07 mg/g roasted.6 Total caffeoylquinic acids showed a general correlation with pH.6\n\nChlorogenic acid lactones are among the main contributors to coffee's bitterness, according to two textbook chapters.2,3 Phenylindanes, formed from these lactones, are linked to a lingering, harsh bitterness in dark roasts.2,3 As chlorogenic acids give way to bitter products, the balance between acidity and bitterness shifts with roast degree.2,7\n\n## Development time at constant colour\n\nRoast degree is not the only factor.5 A 2020 study roasted one Colombian coffee four times in a 1 kg drum roaster to the same colour (Agtron 76).5 Only the development time after first crack differed: 90, 143, 266 and 390 s.5 Acids in the French-press brews were measured by proton NMR.5\n\n
\n
\n
Acids and 5-CQA in the brew after four development times at the same colour (Agtron 76), measured by ¹H NMR; lines only join the measured points.5
\n
\n\nFormic, citric and malic acids fell as development time grew; 5-CQA fell too, but was about the same in the two longest roasts.5 Acetate and lactate stayed within a narrow band, with their lowest values in the longest roast.5 Sensory acidity fell from 8.5 to 5.4 across the four roasts.5 The authors note that the acids were degraded to about the same extent, so the ratio between them did not change. In their reading, development time cannot be used to highlight one acid.5\n\n## Reference values\n\nValues reported in the sources. They depend on the coffee, the roast and the brew; they are not targets.\n\n| Parameter | Value reported | Source |\n|---|---|---|\n| Brew pH, arabica vs robusta | 4.85–5.15 vs 5.25–5.40 | Ginz et al.1 |\n| Brew pH, light roasts, hot and cold brew (six origins) | 4.85–5.13 | Rao & Fuller10 |\n| Extract pH, robusta, 3 min roasts | 6.1 (150 °C); 5.7 (240 °C); 6.3 (280 °C) | Ginz et al.1 |\n| Acids, share of bean weight | About 11% (green); about 6% (roasted) | Ginz et al.1 |\n| Sucrose in green coffee | 3–8% | Ginz et al.1 |\n| Total chlorogenic acids, seven commercial coffees | 34.43–41.64 mg/g (green); 2.05–7.07 mg/g (roasted) | Moon et al.6 |\n| Chlorogenic acids after roasting | Nearly 50% left at 230 °C for 12 min; almost trace at 250 °C for 21 min | Moon et al.6 |\n| Titratable acidity, green coffee (5 kg drum study) | 2.2 ± 0.3 mL 0.1 mol/L NaOH per 40 mL brew (pH 5.9 ± 0.1) | Anokye-Bempah et al.4 |\n| Titratable acidity, peak during first crack | 4.9 ± 0.2 (all profiles and coffees); 4.8 (Uganda), 4.9 (El Salvador), 5.1 (Sumatra) | Anokye-Bempah et al.4 |\n| Titratable acidity at second crack (three profiles, African washed coffee) | 2.5–2.8 | Anokye-Bempah et al.4 |\n| Titratable acidity, end of 16 min roasts | 1.2 ± 0.1 and 1.7 ± 0.2 (two groups of profiles) | Anokye-Bempah et al.4 |\n| Acids in the brew, 90 s vs 390 s development (mM) | Formic 5.53 vs 4.16; citric 4.33 vs 3.73; malic 1.22 vs 0.95; acetate 9.26 vs 8.63; lactate 0.89 vs 0.88 | Alstrup et al.5 |\n| Titration end points used in research | pH 6.6 (about mouth pH) and pH 8.0; pH 8.2 | Gloess et al.9; Anokye-Bempah et al.4 |\n| Sour reference, SCA | 0.04% citric acid (SCA 103-2024); 0.015% (CVA document) | SCA14,15 |\n| Sour reference, two sensory studies | 0.6 g/L citric acid; 1.2 g/L citric acid | Münchow et al.7; Alstrup et al.5 |\n\n## Measuring acidity\n\n- **pH.** Read with a pH meter on the brew or extract. According to the drip-coffee study's lead author, pH varied more between roast degrees than with brewing.8\n- **Titratable acidity.** A fixed volume of brew is titrated with 0.1 mol/L sodium hydroxide to a set end point.4,9 One study titrated to pH 6.6, about the pH in the mouth, and to pH 8.0, which also covers the weaker organic acids.9 A roasting study used pH 8.2 for consistency with earlier drip-coffee work.4 Titratable acidity also rises with brew strength, so the brew recipe belongs with the result.8\n- **Individual acids.** Chromatography, capillary electrophoresis and NMR give single acids.1,5,12 The concentration of one acid does not tell how acidic the cup will taste (see Acidity in cupping).12,15\n\n## Acids in the brew\n\nAccording to a brewing textbook chapter, sugars and acids are highly soluble, so under-extracted coffee is proportionally richer in them and leans towards sweet and acidic notes.17\n\nBrewing method shifts the balance. Hot brews of six light roasts held more titratable acid than cold brews of the same coffees, at comparable pH.10 The authors suggest that hot brewing extracts more acids that are not deprotonated.10\n\nWater changes what reaches the tongue. Alkalinity neutralises part of the extracted acids.11 The water entry covers how much.\n\n## Two species: arabica and robusta\n\nThe sources do not agree on which species carries more acid. A 2000 paper reports lower pH in arabica brews than in robusta brews.1 According to the authors of a meta-analysis, arabica tends to have lower amounts of organic acids, with a minimum at a medium roast.13 In the same analysis, formic acid increased in robusta during roasting.13\n\nFor chlorogenic acids the picture is similar. A roasting chemistry chapter states that robusta green coffee contains significantly more.3 The meta-analysis found the difference not statistically significant over its much larger sample, and similar losses with roasting in both species.13\n\n## Open questions\n\n- **Which acids drive perceived acidity.** No single acid predicts it. In the 2023 conference study only citric acid was clearly detected on its own, and tasters could not identify acids added to coffee.12\n- **pH and titratable acidity versus sourness.** Drip-coffee work favours titratable acidity; a nine-method comparison found neither measure correlated (see Contested).8,9\n- **Acetic acid in dark roasts.** Earlier analyses and a 2023 study disagree (see Contested).1,12\n- **Glycolic and phosphoric acids.** No sensory data for glycolic acid was found; phosphoric acid in coffee rests on one conference abstract in the sources opened.12\n- **Peak timing and colour.** The titratable-acidity study did not measure roast colour, so its peak cannot yet be placed on a colour scale.4\n\n## Key studies\n\n
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Ginz et al., 2000 – Acids from sugars. Soaks robusta beans in sugar solutions, roasts them and runs model roasts of pure sugars, including carbon-13-labelled glucose. Sucrose turns out to be the main green-bean precursor of formic, acetic, glycolic and lactic acid, through known sugar breakdown pathways.

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European Food Research and Technology 211(6), 404–410 · doi:10.1007/s002170000215

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Anokye-Bempah et al., 2024 – Titratable acidity during the roast. Samples beans every minute from up to seven very different 16-minute profiles on a 5 kg drum roaster, using three coffees. Titratable acidity always peaked during first crack and fell back by second crack; the profile changed the timing more than the peak.

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Scientific Reports 14, 8237 · doi:10.1038/s41598-024-57256-y

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Alstrup et al., 2020 – Development time and acids. Roasts one Colombian coffee to the same colour with four development times and measures the brews by NMR and GC–MS. Acids generally declined with longer development, and sensory acidity fell with them.

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Beverages 6(4), 70 · doi:10.3390/beverages6040070

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Moon et al., 2009 – Chlorogenic acids and roasting. Measures nine chlorogenic acid isomers in commercial and laboratory-roasted coffees. Total chlorogenic acids fell with roasting intensity, to nearly half at 230 °C for 12 min and to traces at 250 °C for 21 min.

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Journal of Agricultural and Food Chemistry 57(12), 5365–5369 · doi:10.1021/jf900012b

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Gloess et al., 2013 – Nine brewing methods. Brews one Guatemalan coffee (capsules excepted) by nine methods, from filter coffee to espresso, and compares chemistry with a trained panel. Neither pH nor titratable acidity correlated with perceived acidity across the methods.

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European Food Research and Technology 236, 607–627 · doi:10.1007/s00217-013-1917-x

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