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Roasting · Chemistry

Roasting contaminants

Unwanted compounds that form in coffee during roasting – acrylamide, furan and methylfurans, and traces of polycyclic aromatic hydrocarbons – how roast degree shifts them and what food authorities say and require.

Across the chain: Science

Source-checkedby Coffearium verification pass· Last source-checked 20 Oct 2026· Prepared with AI assistance· 21 sources (18 tier A)· 1 contested· Updated 20 Oct 2026
Reading depth
Contents
  • Acrylamide forms from asparagine and reducing sugars in the Maillard reaction; in roasting it peaks early and then falls as the roast goes darker.2,5,6,7
  • Furan and methylfurans run the other way – darker and longer roasts contain more of them.9,11
  • EU Regulation 2017/2158 sets an acrylamide benchmark level of 400 µg/kg for roast coffee and 850 µg/kg for instant coffee.1
  • The regulation notes that robusta-based products tend to have higher acrylamide levels than arabica-based ones.1
  • One 2023 study concluded that lowering acrylamide and furans at the same time by changing the roast seems not to be possible.9

What roasting contaminants are#

Roasting builds flavour, colour and aroma through chains of chemical reactions. A few products of the same reactions are unwanted. The EU treats acrylamide as a contaminant that forms in food from precursors in the raw material.1 A 2023 review calls such compounds thermal contaminants induced by roasting.14 The roasting chemistry chapter of a 2017 textbook names acrylamide and furan as Maillard-type products to mitigate.19

The best-studied ones in coffee are acrylamide and a group of furans: furan itself and the methylfurans.8,9,14 A 2023 review also lists polycyclic aromatic hydrocarbons (PAHs), 4-methylimidazole and several other groups.14

This entry covers what forms in the coffee itself. Smoke and gases that leave through the stack are covered in roaster emissions. The entry describes what authorities state and require; it gives no health advice.

Acrylamide: made early, broken down later#

Acrylamide forms from sugars and amino acids, mainly asparagine, through the Maillard reaction.2 Green coffee contains both precursors. In one 2021 study, green coffee had no measurable acrylamide; it appeared only on roasting.5

Acrylamide does not simply build up as the roast goes on. It peaks in the lighter roast degrees and then falls as roasting continues.5,6,7,9 In a 2020 industrial roasting study, it peaked after 10 min at 175–177 °C. In the finished coffee it was close to 300 µg/kg, well below the peak.6

020040060080010001200µg/kg acrylamidePilot drum roaster 2021,arabica: peak7305 Pilot drum roaster 2021,robusta: peak1,1305 Industrial roast 2020,arabica: peak1,0456 Industrial roast 2020,robusta: peak7956 Industrial roast 2020,finished coffee≈3006 64 batches 2023, oneprofile: range99.8–558.88 EU benchmark level, roastcoffee4001
Data table
Pointµg/kg acrylamideSource
Pilot drum roaster 2021, arabica: peak7307305
Pilot drum roaster 2021, robusta: peak1,13011305
Industrial roast 2020, arabica: peak1,04510456
Industrial roast 2020, robusta: peak7957956
Industrial roast 2020, finished coffee≈3003006
64 batches 2023, one profile: range99.8–558.899.8–558.88
EU benchmark level, roast coffee4004001
Acrylamide in roasting coffee as reported in three studies: peak values during roasting, the level in one finished industrial roast and the range in 64 batches roasted to one profile, against the EU benchmark level for roast coffee.1,5,6,8 Studies used different coffees and roasters; values do not form one curve.

Robusta (C. canephora) and arabica (C. arabica) coffee differ. The EU regulation on acrylamide states that robusta-based products tend to have higher levels.1 Studies mostly agree, though one industrial study found the opposite at the peak.5,6,8

Furans: rising with roast degree#

Furan and its methylated relatives behave differently. They are volatile compounds, and their sum was higher the darker and the longer the roast in a 2023 study.9 In a 2011 study, furan in espresso brews rose about sixfold from the lightest to the darkest roast.11

2-Methylfuran is the most abundant of them, followed by furan.8,9 Furan is volatile, and part of it can evaporate during roasting and brewing.11 In a Canadian survey, instant coffee and coffee beverages had relatively low levels of furans compared with other coffee products.12

The European Food Safety Authority (EFSA) names coffee as the main source of furan in the diet of adults.10

Other compounds: PAHs, 4-methylimidazole and ochratoxin A#

Polycyclic aromatic hydrocarbons are compounds that form in high-temperature processes such as roasting, smoking and barbecuing.14,15 In a 2019 study, a mild roast lowered PAHs compared with the green coffee.15 A 2023 study found benzo[a]pyrene, a marker PAH, only in two dark-roasted samples.16

4-Methylimidazole forms from sugars reacting with ammonia. A 2023 review reports higher average levels in robusta than in arabica coffee.14

Ochratoxin A is not formed by roasting. It is a mould toxin that can form during drying and storage of green coffee, as the Codex code of practice describes; moisture and water activity covers it.17 The Codex code of practice states that roasting reduces it by 65–100%, depending on the process.17

What a roaster can and cannot change#

The EU regulation asks food business operators to identify the roast conditions that keep acrylamide low within the target flavour profile.1 It also asks them to consider the share of robusta in a blend and the use of asparaginase.1 Asparaginase is an enzyme that breaks down asparagine before roasting.14

These levers pull in different directions. A darker or longer roast lowers acrylamide but raises furans.9 A UK coffee trade code warns that roasting darker cannot be considered a universal option.20 A 2023 study concluded that lowering both at once by roasting changes seems not to be possible.9

Some things lie outside the roaster’s hands. Acrylamide in roasted coffee falls during storage, depending on time and temperature.18 Part of the furan evaporates during brewing, in the cup or the pot.11

Reference values#

Values as reported in the sources. Each study used its own coffees, roaster and analytical method; values are not targets. µg/kg equals ppb (by mass); ng/ml in a brew equals µg/l.

Parameter Value reported Source
EU acrylamide benchmark level, roast coffee 400 µg/kg Regulation 2017/21581
EU acrylamide benchmark level, instant (soluble) coffee 850 µg/kg Regulation 2017/21581
EU benchmark, coffee substitutes from cereals only / chicory only 500 / 4,000 µg/kg; mixtures by proportion Regulation 2017/21581
Acrylamide in green coffee Below the limit of quantification Schouten et al. 20215
Acrylamide peak, pilot drum roaster (250 g batches) 730 ± 30 µg/kg arabica (Brazil), 1,130 ± 10 µg/kg robusta (India), both at light-medium Schouten et al. 20215
Acrylamide fall to dark roast, same study −85% arabica, −88% robusta from the peak; medium to dark below 400 µg/kg Schouten et al. 20215
Acrylamide peak, industrial roast (90 °C to ≈215 °C) At 10 min, 175–177 °C: 1,045 ± 28 µg/kg arabica, 795 ± 25 µg/kg robusta; below 400 µg/kg at 14 min (203–205 °C); ≈300 µg/kg in the final product Bertuzzi et al. 20206
Acrylamide, 64 batches (63 analysed), one profile (80 to 230 °C in 8 min) 99.8–558.8 µg/kg, mean 236.9; robusta mean 329, arabica mean 217 Alsafra et al. 20238
Furans, same batches (mean) 2-Methylfuran 21,000; furan 5,930; 2,5-dimethylfuran 2,170; 3-methylfuran 1,041 µg/kg Alsafra et al. 20238
Sum of furans, arabica ≈10,000 µg/kg in light roasts, up to ≈40,000 µg/kg in longer or darker roasts; across the study, 2-methylfuran ≈70% and furan ≈20% of the sum Engelhardt et al. 20239
Furan, ground and whole-bean coffee, Canadian retail (n = 105) 890–8,800 ppb, mean 4,705 CFIA 202112
Furan, instant coffee, Canadian retail (n = 18) 39–810 ppb, mean 193 CFIA 202112
Total furans, highest single sample 38,670 ppb, dark-roast whole beans CFIA 202112
Furan in brews Drip 20–78 ng/ml; espresso 43–146 ng/ml; instant 12–35 ng/ml; capsules 117–244 ng/ml (Spanish market) Altaki et al. 201111
Furan in drip-brewed coffee, US retail (2004) 33.6–84.2 ppb FDA13
PAHs (19 compounds), mild roast (125–135 °C, 25–26 min) Green 8.66–76.63 µg/kg; roasted 4.29–16.17 µg/kg; benzo[a]pyrene not detected Ciecierska et al. 201915
Benzo[a]pyrene, retail ground coffee Detected in two dark-roasted samples, near the detection limit of 9.0 ng/g Aresta & Zambonin 202316
Ochratoxin A reduction by roasting 65–100%, depending on the process Codex CAC/RCP 69-200917

Acrylamide chemistry#

Precursors. Acrylamide forms from reducing sugars and amino acids, mainly asparagine, in the Maillard reaction.2 The 2023 batch study found acrylamide strongly related to free asparagine, and furans to sucrose more than to the other sugars.8 In the 2021 study, green robusta contained more asparagine than arabica (800 ± 50 versus 540 ± 40 mg/kg) and less reducing sugar.5 Sucrose must first split into glucose and fructose before it can react; the Maillard reaction entry covers that step.19

Formation and elimination. In the 2020 industrial study, asparagine fell quickly, while glucose and fructose peaked at 12 min and then degraded fast.6 The authors attribute the sugar rise mainly to sucrose hydrolysis.6 Acrylamide peaked before the sugars did and fell below 400 µg/kg four minutes later.6 An early oven and laboratory-roaster study reported that beans roasted longer, or at higher temperatures, had less acrylamide.7 A 2023 review places the formation peak in the intermediate stage of roasting, at 160–180 °C.14

Rate at the same colour. A UK trade code, based on a European industry toolbox, states that roasting faster gives higher acrylamide at the same roast colour.20 No study opened for this entry measured acrylamide at one colour across several roast durations with numbers in an accessible text.

After roasting. Acrylamide in roasted coffee decreases during storage, depending on time and temperature.18 In a radiotracer study, close to 90% of the label in spent grounds was firmly bound to the coffee matrix, and furanthiols did not explain the loss.18 According to a decaffeination textbook chapter, acrylamide is formed in roasting and its quantity is not changed by decaffeination or steaming.21

Furan chemistry#

Precursors. EFSA lists ascorbic acid, amino acids and carbohydrates among the precursors of furans, and notes that furan and methylfurans can occur together.10 In coffee, furan levels correlated with sucrose.8 The roasting chemistry chapter warns that model systems may not predict how furan forms in a roasting bean.19

Roast degree and rate. In the 2011 study, furan in espresso brews rose from 22 ± 2 to 138 ± 8 ng/ml as L* fell from 47.4 to 23.16.11 At one colour, a slow roast at 140 °C for 20 min gave the lowest level (64 ± 5 ng/ml); faster, hotter roasts gave 89 and 138 ng/ml.11 The authors suggest more furan evaporated during the long roast.11 In the 2023 roasting study, steam-treated and water-cooled samples were lower in furans.9

Losses before the cup. Furan is volatile.11 In the 2011 study, espresso brews held 32–85% more furan than drip brews from the same coffees, which the authors link to shorter contact and higher pressure.11 No study opened for this entry measured the furan lost on grinding.

PAHs and 4-methylimidazole#

PAHs. In the 2019 study, pyrolytic reactions begin above 170 °C; some PAHs form above 220 °C and heavier ones from 250–260 °C.15 Its mild roast lowered total PAHs, which the authors attribute to the volatility of light PAHs.15 The authors name drying and roasting as probably the main sources of PAHs in coffee.15 In the 2023 retail study, chrysene and pyrene dominated, which the authors read as a probable sign of roasting at 280 °C or more.16 A 2023 review states that longer roasting raises high-molecular-weight PAHs.14 No study opened for this entry compared PAHs in coffee from direct-fired and indirectly heated roasters.

4-Methylimidazole. The 2023 review describes its formation from sugars and ammonia and higher average levels in robusta.14 No study opened for this entry reported its levels in roasted coffee with accessible numbers.

Authorities and regulation#

Rules and assessments as opened on 20 October 2026. The legal text in force applies.

EU acrylamide regulation. Regulation (EU) 2017/2158 defines benchmark levels as performance indicators used to verify the effectiveness of the mitigation measures.1 They are based on experience and occurrence for broad food categories.1 For coffee, the regulation requires operators to identify critical roast conditions and to control them in a prerequisite programme under good manufacturing practice.1 It asks them to consider asparaginase treatment where possible and effective, and to take robusta’s higher levels into account in blend risk assessment.1 Its recitals describe acrylamide as a contaminant and a chemical hazard in the food chain, formed in foods whose raw materials include coffee beans.1

01000200030004000µg/kg acrylamide (benchmark level)Roast coffee4001 Instant (soluble) coffee8501 Coffee substitutes fromcereals only5001 Coffee substitutes fromchicory only4,0001
Data table
µg/kg acrylamide (benchmark level)Source
Roast coffee4001
Instant (soluble) coffee8501
Coffee substitutes from cereals only5001
Coffee substitutes from chicory only4,0001
Acrylamide benchmark levels for coffee and coffee substitutes set by Commission Regulation (EU) 2017/2158 (Annex IV). For substitutes that mix cereals and chicory, the level depends on the proportions. Benchmark levels are performance indicators, not maximum levels.1

EFSA on acrylamide (2015). EFSA found the highest acrylamide levels in solid coffee substitutes and coffee, and in fried potato products.3 It found that epidemiological associations had not shown acrylamide to be a human carcinogen, but that the margins of exposure indicate a concern for neoplastic effects based on animal evidence.3 The International Agency for Research on Cancer (IARC) classified acrylamide in 1994 as probably carcinogenic to humans (Group 2A).4

EFSA on furan and methylfurans (2017). In adults and older people, coffee is the main contributor to dietary exposure to furan.10 EFSA concluded that the calculated margins of exposure indicate a health concern.10 The US Food and Drug Administration (FDA) describes furan as possibly carcinogenic to humans, based on high-dose animal tests.13 The CFIA reports that maximum levels for furans have not yet been established in Canada; Health Canada did not expect the levels in the survey to pose a health concern.12

PAHs and 4-methylimidazole. A 2023 review states that no maximum limits for PAHs are set for coffee, and a 2023 analytical paper says the same for coffee beverages, as of their writing.14,16 The review reports that IARC classifies 4-methylimidazole as possibly carcinogenic to humans (Group 2B).14

Mitigation options#

  • Roast degree and time. Longer and darker roasting lowers acrylamide.5,7,9 It raises furans.9,11
  • Blend. A lower robusta share is one factor the EU regulation asks operators to consider.1
  • Asparaginase. A 2023 review cites studies reporting a 60% reduction of asparagine in arabica and 35% in robusta, and a 59% reduction of acrylamide in arabica, from enzyme treatment.14 The UK trade code gives the treatment potential relevance for only a very modest fraction of coffee production.20
  • Special processes. The 2023 review lists vacuum and superheated-steam roasting, supercritical CO₂ extraction and acrylamide-degrading enzymes, and notes that cost, scale-up and sensory effects are often unstudied.14 In one 2023 study, double roasting cut acrylamide in light roasts by up to 36%.9
  • Cooling. In the same study, water quenching of a light robusta roast gave 543 µg/kg acrylamide against 371 µg/kg with air cooling.9 The cooling and quenching entry covers the methods.

Measurement#

The 2023 roasting study measured acrylamide by GC-MS/MS after derivatisation (DIN EN ISO 18862), with acrylamide-d3 as internal standard.9 Furans were measured by headspace GC-MS with deuterated standards.9 Because furans are volatile, the 2011 study stored samples sealed at 4 °C and brews in vials without headspace.11

Open questions#

  • Acrylamide and furans together. One 2023 study found no roasting change that lowered both.9 Whether a profile exists that lowers both within a given flavour target was not found in the sources opened.
  • Roast rate at one colour. Numeric data on acrylamide for fast and slow roasts to the same colour were not found in an accessible text for this entry.
  • Shop-scale roasters. The studies opened used pilot, laboratory or industrial roasters; none measured contaminants on roasters of a few kilograms per batch.
  • Heating type and PAHs. No study opened for this entry compared direct-fired and indirect roasters.
  • 4-Methylimidazole levels. No accessible measurements in roasted coffee were found for this entry.

Key studies#

Schouten et al., 2021 – Acrylamide across five roast degrees. Roasted Brazilian arabica and Indian robusta coffee from light to dark on a pilot drum roaster and followed acrylamide and antioxidant activity. Acrylamide peaked at the light-medium degree, higher in robusta, and fell by more than 80% to the dark roast.

Food Chemistry 343, 128514 · doi:10.1016/j.foodchem.2020.128514

Bertuzzi et al., 2020 – Acrylamide in an industrial roaster. Sampled arabica and robusta coffee during industrial roasting and measured acrylamide, asparagine and sugars. Acrylamide peaked at 10 min, at 175–177 °C, and the finished coffee held about 300 µg/kg.

Food Chemistry, 125372 · doi:10.1016/j.foodchem.2019.125372

Alsafra et al., 2023 – Precursors behind the contaminants. Roasted 64 batches of green coffee to one profile and related acrylamide and four furans to sugars and amino acids by multivariate statistics. Acrylamide followed free asparagine; furans followed sucrose.

Food Chemistry 427, 136655 · doi:10.1016/j.foodchem.2023.136655

Engelhardt et al., 2023 – Acrylamide and furans move in opposite directions. Roasted robusta and arabica coffee on tangential, drum and hot-air roasters with several profiles and pretreatments. Acrylamide was highest in light roasts and furans in dark and long roasts; the authors concluded that lowering both at once seems not to be possible.

Beverage Plant Research 3, 8 · doi:10.48130/BPR-2023-0008

Altaki et al., 2011 – Furan from roaster to cup. Measured furan in coffees roasted to different degrees and rates and in brews from espresso machines, drip makers, capsules and instant coffee. Furan rose with roast degree, was lowest after a slow roast, and was higher in espresso than in drip brews.

Food Chemistry 126(4), 1527–1532 · doi:10.1016/j.foodchem.2010.11.134

Contested
  • Arabica versus robusta at the acrylamide peak: in a 2021 pilot-roaster study, robusta peaked higher than arabica (1,130 versus 730 µg/kg)5, and in a 2023 study of 64 batches robusta averaged more (329 versus 217 µg/kg)8; in a 2020 industrial roasting study arabica peaked higher (1,045 versus 795 µg/kg).6 The EU regulation states that robusta-based products tend to have higher levels.1
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Change log

  • – The furan values across roast degree and rate in the 2011 study are now marked as measured in espresso brews. Reason: Verification; Altaki et al. 2011 prepared these brews with an espresso machine.
  • – "Furans are partly lost while the brew stands" replaced by evaporation during brewing. Reason: Verification; Altaki et al. 2011 describe evaporative loss during brewing in the cup or pot and did not measure losses while a brew stands.
  • – The UK trade code is now quoted as giving asparaginase treatment potential relevance for only a very modest fraction of production; "expects modest effects" removed. Reason: Verification; the code does not describe the size of the effect.
  • – "No maximum levels for furans" is now limited to Canada; the 70% and 20% furan shares in Engelhardt et al. 2023 are no longer given as arabica-only; the brief now says the study concluded that lowering both "seems not to be possible". Reason: Verification; wording was broader or stronger than the sources (CFIA 2021, Engelhardt et al. 2023).

Sources

  1. AEuropean Commission (2017). Commission Regulation (EU) 2017/2158 of 20 November 2017 establishing mitigation measures and benchmark levels for the reduction of the presence of acrylamide in food. Official Journal of the European Union L 304, 21 November 2017 (EUR-Lex).
  2. AEuropean Food Safety Authority (EFSA) Acrylamide (topic page). EFSA.
  3. AEFSA Panel on Contaminants in the Food Chain (CONTAM) (2015). Scientific Opinion on acrylamide in food. EFSA Journal 13(6), 4104. doi:10.2903/j.efsa.2015.4104 · other copies
  4. AInternational Agency for Research on Cancer (IARC) (1994). Acrylamide (IARC Summary & Evaluation, Volume 60, 1994). IARC Monographs on the Evaluation of Carcinogenic Risks to Humans 60, p. 389 (via IPCS INCHEM).
  5. ASchouten, M. A.; Tappi, S.; Angeloni, S.; Cortese, M.; Caprioli, G.; Vittori, S.; Romani, S. (2021). Acrylamide formation and antioxidant activity in coffee during roasting – A systematic study. Food Chemistry 343, 128514 (accepted manuscript). doi:10.1016/j.foodchem.2020.128514 · other copies
  6. ABertuzzi, T.; Martinelli, E.; Mulazzi, A.; Rastelli, S. (2020). Acrylamide determination during an industrial roasting process of coffee and the influence of asparagine and low molecular weight sugars. Food Chemistry 303, 125372. doi:10.1016/j.foodchem.2019.125372 · other copies
  7. ABagdonaite, K.; Murkovic, M. (2004). Factors Affecting the Formation of Acrylamide in Coffee. Czech Journal of Food Sciences 22 (Special Issue), S22–S24. doi:10.17221/10604-CJFS · other copies
  8. AAlsafra, Z.; Kuuliala, L.; Scholl, G.; Saegerman, C.; Eppe, G.; De Meulenaer, B. (2023). Characterizing the formation of process contaminants during coffee roasting by multivariate statistical analysis. Food Chemistry 427, 136655. doi:10.1016/j.foodchem.2023.136655 · other copies
  9. AEngelhardt, U. H.; Bahar, I.; Delker, U. (2023). Food borne toxicants in coffee: Acrylamide and furan derivative content in Arabica and Robusta coffees with different roasting profiles and varying degrees of roast. Beverage Plant Research 3, 8. doi:10.48130/BPR-2023-0008 · other copies
  10. AEFSA Panel on Contaminants in the Food Chain (CONTAM) (2017). Risks for public health related to the presence of furan and methylfurans in food. EFSA Journal 15(10), 5005. doi:10.2903/j.efsa.2017.5005 · other copies
  11. AAltaki, M. S.; Santos, F. J.; Galceran, M. T. (2011). Occurrence of furan in coffee from Spanish market: Contribution of brewing and roasting. Food Chemistry 126(4), 1527–1532. doi:10.1016/j.foodchem.2010.11.134 · other copies
  12. ACanadian Food Inspection Agency (CFIA) (2021). Furan, 2-methylfuran and 3-methylfuran in Selected Foods – April 1, 2020 to March 31, 2021. CFIA, Food chemistry – Targeted surveys – Final report.
  13. AU.S. Food and Drug Administration (FDA) Exploratory Data on Furan in Food. FDA (data tables 2004–2008).
  14. Ada Costa, D. S.; Albuquerque, T. G.; Costa, H. S.; Bragotto, A. P. A. (2023). Thermal Contaminants in Coffee Induced by Roasting: A Review. International Journal of Environmental Research and Public Health 20(8), 5586. doi:10.3390/ijerph20085586 · other copies
  15. ACiecierska, M.; Derewiaka, D.; Kowalska, J.; Majewska, E.; Drużyńska, B.; Wołosiak, R. (2019). Effect of mild roasting on Arabica and Robusta coffee beans contamination with polycyclic aromatic hydrocarbons. Journal of Food Science and Technology 56(2), 737–745. doi:10.1007/s13197-018-3532-0 · other copies
  16. AAresta, A. M.; Zambonin, C. (2023). Determination of Polycyclic Aromatic Hydrocarbons (PAHs) in Coffee Samples by DI-SPME-GC/MS. Food Analytical Methods. doi:10.1007/s12161-023-02463-y · other copies
  17. ACodex Alimentarius Commission (FAO/WHO) (2009). Code of Practice for the Prevention and Reduction of Ochratoxin A Contamination in Coffee (CAC/RCP 69-2009). Codex Alimentarius.
  18. ABaum, M.; Böhm, N.; Görlitz, J.; Lantz, I.; Merz, K. H.; Ternité, R.; Eisenbrand, G. (2008). Fate of 14C-acrylamide in roasted and ground coffee during storage. Molecular Nutrition & Food Research 52(5), 600–608. doi:10.1002/mnfr.200700413 · other copies
  19. BPoisson, L.; Blank, I.; Dunkel, A.; Hofmann, T. (2017). The Chemistry of Roasting – Decoding Flavor Formation. In: Folmer, B. (ed.), The Craft and Science of Coffee, Academic Press, ch. 12, pp. 273–309. doi:10.1016/B978-0-12-803520-7.00012-8 · other copies
  20. BBritish Coffee Association (2019). Sector Code of Practice for Managing Acrylamide Formation in Coffee (version 1, June 2019). British Coffee Association (based on the FoodDrinkEurope Acrylamide Toolbox 2018).
  21. BPietsch, A. (2017). Decaffeination – Process and Quality. In: Folmer, B. (ed.), The Craft and Science of Coffee, Academic Press, ch. 10, pp. 225–243. doi:10.1016/B978-0-12-803520-7.00010-4 · other copies

Tier A · authoritative · B · trade and expert · C · general. Supporting quotes for every source are in the data version of this entry. If a publisher’s site refuses access, try the doi link or “other copies”.

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