{ "id": "browning-phase", "url": "https://coffearium.org/entries/browning-phase/", "license": "CC-BY-4.0", "title": "Browning phase", "summary": "The stretch of a roast between yellowing and first crack, often called the Maillard phase – when the bean darkens fastest, loses most of its sucrose, forms new acids and aroma, and builds up the gas that ends in first crack.", "domain": "roasting", "kind": "Process", "stage": "roast", "topics": [ "science" ], "topicSections": {}, "lang": "en", "status": "verified", "reviewer": "Coffearium verification pass", "lastVerified": "2026-10-17T00:00:00.000Z", "updated": "2026-10-17T00:00:00.000Z", "added": "2026-10-17T00:00:00.000Z", "brief": [ "In roasting practice, the span from the visible colour change to first crack is called the Maillard phase; browning reactions start before it and continue after it.1,6,13", "In one study of 39 drum roasts, ground-coffee lightness (L*) fell from 62.38 at colour change to 29.74 at first crack, whatever the profile or origin.2", "In a 2019 time-course study, sucrose fell from 70.1 to 14.3 mg/g (dry weight) between the start and minute 9 of a 14 min roast.3", "In a 5 kg drum, this phase lasted 2.5–7.5 min across seven profiles; titratable acidity rose through it and peaked at first crack.1", "No peer-reviewed sensory study opened for this entry varied this phase on its own; time to first crack, which includes it, affected flavour less than development time.9" ], "quickFacts": [ { "label": "Starts", "value": "At the visible colour change (yellowing)" }, { "label": "Ends", "value": "At first crack" }, { "label": "Also called", "value": "Maillard phase; colour change to first crack" }, { "label": "Colour (ground, L*)", "value": "62.38 → 29.74 from colour change to first crack (one study, 39 roasts)" }, { "label": "Duration", "value": "2.5–7.5 min in seven profiles on a 5 kg drum (one study)" }, { "label": "Main chemical changes", "value": "Sucrose and chlorogenic acids fall; formic, acetic and lactic acids rise; aroma volatiles appear" }, { "label": "Separate sensory evidence", "value": "None found for this phase on its own" } ], "aka": [ "Maillard phase", "Colour change to first crack", "Yellowing to first crack" ], "linkTerms": [ "browning phase", "Maillard phase", "colour change to first crack", "color change to first crack", "yellowing" ], "related": [ "preheating-and-charge", "drying-phase", "first-crack", "development-time", "second-crack", "roast-profile", "roasting", "maillard-reaction", "acids-in-coffee", "roast-degree-and-colour", "roast-defects", "roast-loss", "degassing", "drum-roaster" ], "contested": [ "When the roast turns exothermic: in real-time exhaust data from one drum roast, the authors placed the change from endothermic drying to the exothermic phase at 625 s, before first crack at about 730 s4; a roasting textbook chapter ties the switch to first crack11; a heat-transfer model places exothermic reactions from nearly 200 °C.7 See also the roasting overview.", "What builds the pressure that ends this phase: a 2020 sensory study describes first crack as accumulated steam pressure cracking the beans9; a roasting textbook chapter names gas together with water vapour as the driving force for expansion11; in a fluid-bed study, carbon dioxide from reactions rose clearly only once the bean core reached 180–200 °C.5", "Lengthening the Maillard phase: some roasters design profiles to spend more time in it, while a practitioner course calls the benefit doubtful13; a 2024 study notes that an extended Maillard profile is thought to reduce sweetness and give flat or baked flavours, citing a roasting reference, but measured only acidity.1" ], "corrections": [], "sources": [ { "id": "s1", "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": "This phase is commonly referred to as the Maillard phase since many roasters associate the browning with Maillard reactions", "accessed": "2026-10-17T00:00:00.000Z" }, { "id": "s2", "title": "A universal color curve for roasted arabica coffee", "authors": "Anokye-Bempah, L.; Styczynski, T.; Ristenpart, W. D.; Donis-González, I. R.", "year": 2025, "publisher": "Scientific Reports 15, 24192", "url": "https://www.nature.com/articles/s41598-025-06601-w", "doi": "10.1038/s41598-025-06601-w", "tier": "A", "tierNote": "Read in full, with its correction (Sci. Rep. 15, 35559, 2025), which changes only the Figure 4 axis labels and three reference numbers; no values are affected.", "quote": "melanoidin formation resulting from nonenzymatic browning reactions such as the Maillard reaction", "accessed": "2026-10-17T00:00:00.000Z" }, { "id": "s3", "title": "The effect of coffee beans roasting on its chemical composition", "authors": "Diviš, P.; Pořízka, J.; Kříkala, J.", "year": 2019, "publisher": "Potravinarstvo Slovak Journal of Food Sciences 13(1), 344–350", "url": "https://potravinarstvo.com/journal1/index.php/potravinarstvo/article/download/1062/807", "doi": "10.5219/1062", "tier": "A", "quote": "The results show that sucrose degradation occurs during the roasting process.", "accessed": "2026-10-17T00:00:00.000Z" }, { "id": "s4", "title": "Online monitoring of coffee roasting by proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS): towards a real-time process control for a consistent roast profile", "authors": "Wieland, F.; Gloess, A. N.; Keller, M.; Wetzel, A.; Schenker, S.; Yeretzian, C.", "year": 2012, "publisher": "Analytical and Bioanalytical Chemistry 402(8), 2531–2543", "url": "https://digitalcollection.zhaw.ch/bitstream/11475/5554/2/2012_Flurin-etal_Online-monitoring-of-coffee-roasting-by-PTR-ToF-MS.pdf", "doi": "10.1007/s00216-011-5401-9", "tier": "A", "quote": "Until 500 s, the intensities of the VOCs are low and hardly any of the typical coffee aroma compounds are observed.", "accessed": "2026-10-17T00:00:00.000Z" }, { "id": "s5", "title": "Carbon Dioxide Evolution and Moisture Evaporation During Roasting of Coffee Beans", "authors": "Geiger, R.; Perren, R.; Kuenzli, R.; Escher, F.", "year": 2005, "publisher": "Journal of Food Science 70(2), E124–E130", "url": "https://ift.onlinelibrary.wiley.com/doi/10.1111/j.1365-2621.2005.tb07084.x", "doi": "10.1111/j.1365-2621.2005.tb07084.x", "tier": "A", "quote": "As illustrated in Figure 9, the required product temperature to start the chemical reactions was 180°C to 200°C.", "accessed": "2026-10-17T00:00:00.000Z" }, { "id": "s6", "title": "Use of colour parameters for roasted coffee assessment", "authors": "Bicho, N. C.; Leitão, A. E.; Ramalho, J. C.; Lidon, F. C.", "year": 2012, "publisher": "Ciência e Tecnologia de Alimentos 32(3), 436–442", "url": "https://www.redalyc.org/pdf/3959/395940113004.pdf", "doi": "10.1590/S0101-20612012005000068", "tier": "A", "quote": "Around 150 °C, gaseous substances (water vapour, carbon dioxide, and carbon monoxide) are released", "accessed": "2026-10-17T00:00:00.000Z" }, { "id": "s7", "title": "A heat and mass transfer study of coffee bean roasting", "authors": "Fadai, N. T.; Melrose, J.; Please, C. P.; Schulman, A.; Van Gorder, R. A.", "year": 2017, "publisher": "International Journal of Heat and Mass Transfer 104, 787–799", "url": "https://ora.ox.ac.uk/objects/uuid:c2433f0b-fc40-4d7c-a207-5453349f6f91/files/m2e0c0e8fb121aa744f0a35396a18ff60", "doi": "10.1016/j.ijheatmasstransfer.2016.08.083", "tier": "A", "quote": "The resulting high gas pressure causes the cells to expand.", "accessed": "2026-10-17T00:00:00.000Z" }, { "id": "s8", "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": "The initial lower reactivity of sucrose can be attributed to its glycoside linkage which must be cleaved in order to yield the more reactive reducing sugars.", "accessed": "2026-10-17T00:00:00.000Z" }, { "id": "s9", "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": "The results indicated that, while both parameters significantly affected coffee flavour, colour was the stronger predictor of the two.", "accessed": "2026-10-17T00:00:00.000Z" }, { "id": "s10", "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": "Typically, the roast master starts the roast with close to maximum power output from the burner (heat source), and later performs stepwise reductions in the power output to slow down the speed of browning reactions as the roast progresses.", "accessed": "2026-10-17T00:00:00.000Z" }, { "id": "s11", "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": "The gas together with the water vapor constitutes the driving force for bean expansion during roasting.", "accessed": "2026-10-17T00:00:00.000Z" }, { "id": "s12", "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": "Arabinose branches and CGA are degraded in a later stage.", "accessed": "2026-10-17T00:00:00.000Z" }, { "id": "s13", "title": "HTR 4.02 Phases of the Roasting Profile (How to Roast course)", "authors": "Barista Hustle", "publisher": "Barista Hustle (online course)", "url": "https://baristahustle.com/?p=474554", "tier": "C", "quote": "The 'Maillard phase' refers to the time between yellowing and the onset of first crack.", "accessed": "2026-10-17T00:00:00.000Z" } ], "markdown": "## Where the browning phase sits\n\nThe browning phase is step 3 of a roast. It begins when the beans visibly change colour and ends at first crack, the first popping sound.1 Before it comes the drying phase, from charge to colour change; after it comes development, from first crack to the end of the roast.1\n\nStudies name the phases by what the beans show, not by a probe temperature. A 2024 drum-roaster study calls this phase \"colour change to first crack\".1 Colour change is the moment the roaster sees that the bean has clearly changed from its original colour.2 First crack is marked by sight and sound.2 Probe readings at these moments depend on the machine (see Roast profiles).11\n\nPrevious step: drying phase. Next step: first crack.\n\n## Why it is called the Maillard phase\n\nIn roasting practice, the span from yellowing to first crack is called the \"Maillard phase\".13 Many roasters link the browning they see with Maillard reactions, the reactions between sugars and amino acids.1\n\nThe name is a simplification, for three reasons:\n\n- **Browning starts earlier.** Browning through Maillard and Strecker reactions is described as starting above 100 °C.6\n- **Browning goes on later.** Maillard reactions are known to continue after first crack.1 After first crack, browning moves faster, from the surface towards the centre.10\n- **Other reactions run alongside.** Caramelisation, pyrolysis (breakdown by heat) and the breakdown of chlorogenic acids also take place during roasting.11,12\n\nSo the name marks a stretch of the roast, not the limits of one reaction. The chemistry itself is explained in the entry on the Maillard reaction.\n\n## What changes in colour\n\nAccording to a roasting textbook chapter, the bean turns from greenish grey-blue to yellow, orange and brown during roasting.11 Much of that darkening happens in this phase.\n\nA 2025 study measured the colour of ground samples from 39 roasts on a 5 kg drum roaster.2 It used L*, a lightness scale where higher numbers mean lighter. At colour change, L* averaged 62.38; at first crack, 29.74.2 The values at these milestones were about the same for every profile and every coffee tested.2 Of the total fall in lightness from colour change to the end of the roast, about 72% came before first crack (our calculation).2\n\n
\n
\n
Mean lightness (L*) of ground coffee at four roast milestones, pooled over 39 roasts on a 5 kg drum. The browning phase spans the first two bars.2
\n
\n\nThe authors attribute the colour change to melanoidins, brown compounds formed by browning reactions such as the Maillard reaction.2 The same chapter describes colour as closely tied to flavour and as the best indicator of roast degree.11\n\n## What changes inside the bean\n\n**Sugar.** Sucrose is the main free sugar in green coffee.12 In a 2000 study, added sucrose reacted more slowly at first than added glucose or fructose. The authors attribute this to the bond that must split to give the more reactive sugars.8 In a 2019 study, sucrose fell from 70.1 to 14.3 mg/g (dry weight) in the first 9 min of a 14 min roast.3\n\n**Acids.** Chlorogenic acids, a large group of acids in green coffee, break down. In the same study, the measured chlorogenic acid fell from 22.7 to 12.2 mg/g by minute 9.3 At the same time, sugars form new acids, such as acetic and formic acid.3,8 In a 5 kg drum, titratable acidity (the total acid that can be neutralised) rose through the roast and peaked at first crack.1\n\n**Aroma.** In exhaust measurements of one drum roast, hardly any typical coffee aroma compounds appeared before 500 s; first crack came at about 730 s.4 From 500 s on, most traces rose strongly until the end of the roast.4\n\n**Gas and swelling.** Around 150 °C, the bean releases water vapour, carbon dioxide and carbon monoxide, and its volume increases.6 According to a roasting textbook chapter, gas and water vapour together drive the expansion.11 The pressure eventually cracks the bean at first crack.9\n\n
\n
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Sucrose and chlorogenic acid in arabica beans sampled during one medium roast (210 °C, 14 min, 25 g in a home roaster); mg/g dry weight. First crack was not recorded; lines join the measured points only.3
\n
\n\n## How roasters steer this phase\n\nRoasters change the length of this phase with the heat they apply. A specialty roast typically starts near maximum burner output, then steps the power down to slow the browning reactions.10\n\nSome roasters design profiles to spend more time in the Maillard phase. A practitioner course calls the benefit doubtful, because Maillard reactions are not limited to it.13 No peer-reviewed sensory study opened for this entry changed this phase on its own and tasted the result. What studies did find is in the Deep dive.\n\n\n\n## Reference values\n\nValues reported in the sources. They describe particular coffees, roasters and profiles; they are not targets.\n\n| Parameter | Value reported | Source |\n|---|---|---|\n| Definition used in research | \"Colour change to first crack\"; colour change = beans visibly altered from greenish yellow to yellowish brown | Anokye-Bempah et al. 20241 |\n| Duration, seven profiles, one washed African coffee, 5 kg drum, 4 kg batch, 16 min roasts | 2.5–7.5 min (fast start 3.5, slow start 4.0, medium 4.0, production 4.5, exaggerated flick 3.5, negative rate of rise 2.5, extended Maillard 7.5) | Anokye-Bempah et al. 20241 |\n| Mean rate of rise in this phase, same roasts | 2.80–7.72 °C per 30 s (fast start 5.39, slow start 5.79, medium 5.51, production 4.56, exaggerated flick 5.97, negative rate of rise 7.72, extended Maillard 2.80) | Anokye-Bempah et al. 20241 |\n| Mean rate of rise before colour change, same roasts | 5.07–7.98 °C per 30 s | Anokye-Bempah et al. 20241 |\n| Duration, all 13 roast types (three coffees) | 2.5–7.5 min; mean rate of rise 2.79–7.72 °C per 30 s | Anokye-Bempah et al. 20241 |\n| Titratable acidity, green coffee → peak at first crack | 2.2 ± 0.3 → 4.9 ± 0.2 mL NaOH per 40 mL sample (peak: mean of all profiles and coffees) | Anokye-Bempah et al. 20241 |\n| Colour of ground coffee, CIELAB (mean) | Colour change: L* 62.38 ± 2.6, a* 9.62 ± 1.26, b* 30.85 ± 0.86. First crack: L* 29.74 ± 1.9, a* 12.56 ± 0.78, b* 18.92 ± 2.53. Second crack: L* 19.96 ± 1, a* 6.41 ± 1.02, b* 6.45 ± 1.41. End: L* 17.19 ± 1.6 | Anokye-Bempah et al. 20252 |\n| Sucrose, medium roast (210 °C, 14 min), mg/g dry weight, at 0, 4, 5 … 14 min | 70.1, 58.5, 57.0, 50.1, 38.8, 23.8, 14.3, 12.2, 6.3, 4.4, 4.1, 3.0 | Diviš et al. 20193 |\n| Chlorogenic acid, same roast, mg/g dry weight, at 0, 4, 5 … 14 min | 22.7, 17.8, 15.7, 14.5, 13.6, 13.7, 12.2, 11.7, 10.4, 8.9, 7.9, 7.2 | Diviš et al. 20193 |\n| Acetic and formic acid, same roast, mg/g dry weight | Acetic 0.345 (green), 1.07 (8 min), 2.17 (14 min); formic below 0.005 (green), 0.291 (8 min), 0.875 (14 min) | Diviš et al. 20193 |\n| Exhaust volatiles, 15.6 kg batch, medium-temperature dark roast (894 s in the text; 907 ± 3 s in the paper's table of profiles) | Low until 500 s; one trace first seen before 400 s, another just before 500 s; maximum or plateau at about 730 s, with first crack | Wieland et al. 20124 |\n| Gas release and swelling begin | Around 150 °C | Bicho et al. 20126 |\n| Reaction CO₂ and water rise clearly | 180–200 °C, bean core (laboratory fluid bed) | Geiger et al. 20055 |\n| Time to first crack, seven sensory studies | 7:21–10:07 min | Münchow et al. 20209 |\n\n## Timing of the chemistry\n\nThe sources agree on the order of events more than on temperatures. According to a roasting chemistry chapter, sucrose and free amino acids react first, because they are immediately available and highly reactive; arabinose from cell-wall polysaccharides and chlorogenic acids are degraded later, because they first need to be released.12 A 2000 study found glucose and fructose in roasted robusta beans enriched with sucrose, and read reducing-sugar formation as an early step in sucrose breakdown.8\n\n**Sucrose.** The 2019 time course shows the loss is not even. In the medium roast, sucrose fell slowly to 50.1 mg/g at 6 min, then fastest between 6 and 9 min, to 14.3 mg/g; by 14 min it was 3.0 mg/g.3 In both roasts studied, 96–98% of the sucrose was degraded by the end.3 First crack was not recorded. The authors suggest that two sharp maxima of 5-hydroxymethylfurfural could correspond to first and second crack3; in the medium roast these lie at 9 and 13 min in their table.3 If that reading holds, about four-fifths of the sucrose was gone by first crack (our calculation).\n\n**Chlorogenic acids.** They fell more steadily: in the medium roast by 45% in the middle of the roast and by 67% at the end.3 According to the roasting chemistry chapter, their breakdown gives quinic acid, phenolic acids, lactones and volatile phenols such as guaiacol (see Acids in coffee).12\n\n**New acids.** Sucrose is the principal green-coffee precursor of formic, acetic, glycolic and lactic acid.8 In the 2019 study, acetic acid tripled from the green value by minute 8 and formic and lactic acid rose from below 0.005 mg/g.3 In a 5 kg drum, titratable acidity peaked at first crack in every profile and coffee, and the peak was insensitive to how quickly the roast got there.1 In the extended Maillard profile, acidity rose relatively slowly during this phase.1\n\n**Aroma.** In real-time exhaust data of a 15.6 kg drum roast, volatile intensities were low until 500 s. One trace appeared before 400 s and another just before 500 s; both rose until about 730 s, when first crack began, and then either peaked or levelled off.4 According to the textbook chapter on roasting, summarising a 2002 study, most aroma compounds formed fastest at medium roast stages, at bean water contents of 7% to 2% (wet basis).11 According to the roasting chemistry chapter, diketones and furfurals form early, alongside the use of free sugars and amino acids.12\n\n**Maillard, caramelisation and pyrolysis together.** The roasting chapter lists the Maillard reaction, Strecker degradation, pyrolysis and caramelisation among the reactions of carbohydrates during roasting.11 Where caramelisation begins in the bean is disputed (see Maillard reaction). A 2020 sensory paper describes the heat late in the roast as taking the beans into a state of pyrolysis.9 None of the sources opened assigns a fixed share of the browning to one reaction in this phase.\n\n## Water, gas and pressure\n\n**Water.** The phase starts with the beans still drying. One heat-transfer model predicts a sharp drying front that divides the bean into a dry outer region and a moist core.7 The same paper describes a ridge of high-pressure water vapour near the drying front.7\n\n**Carbon dioxide.** According to the roasting chapter, gas formation in isothermal roasting is low at first and accelerates strongly in the second half of the roast.11 In a laboratory fluid bed with a thermocouple in the bean core, carbon dioxide and water from reactions rose significantly only once the core reached 180–200 °C.5 On that evidence, most reaction gas forms towards the end of this phase and after it (our reading). Strecker degradation, decarboxylation of amino acids, the Maillard reaction and the breakdown of chlorogenic acids and sucrose are named as sources.5\n\n**Pressure and expansion.** High gas pressure makes the cells expand.7 According to the roasting chapter, the thick cell walls stretch rather than break, and they expand while in a soft, rubbery state; how far the bean expands therefore depends on the profile.11 Porosity rises gradually as the bean swells.11 Estimates of the internal pressure differ, and no peer-reviewed measurement was found (see the roasting overview).\n\n**Endothermic to exothermic.** Early in the roast, much energy goes into evaporating water; later the process becomes progressively more exothermic.9 Where in the roast this happens is contested. In the exhaust study, the authors placed the transition at 625 s, before first crack.4 A textbook chapter ties it to first crack.11\n\n## Rate of rise in this phase\n\nThe rate of rise (RoR) is how fast the bean-probe reading climbs, here in °C per 30 s (see Roast profiles).1 In the 2024 drum study, the mean RoR in this phase was lower than before colour change in six of seven profiles; only in the slow-start profile was it higher (5.79 against 5.07 °C per 30 s).1\n\nLength and RoR went together. The extended Maillard profile moved quickly through drying and then spent 7.5 min in this phase at a mean RoR of 2.80 °C per 30 s.1 The negative-rate-of-rise profile crossed it in 2.5 min at 7.72 °C per 30 s.1 A 2025 colour study by the same group, of 39 roasts of the same three coffees, found about the same colour at first crack in all roasts2; so the profile changed how fast the beans got there, not where they arrived.\n\n
\n
\n
Duration of the phase from colour change to first crack, with its mean rate of rise, in seven roast profiles of one washed African coffee (5 kg drum, 4 kg batch, 16 min roasts).1
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\n\n## What controlling this phase changes in the cup\n\n**What studies found.** A 2020 analysis of seven sensory studies at constant colour split the roast into time to first crack and development time.9 Time to first crack, which includes drying and this phase together, significantly affected five of nine attributes; development time affected all nine, mostly at higher levels of significance.9 Longer time to first crack went with less acidity and more bitterness, with no significant effect on sweetness.9 Body was not affected by either phase, against a common belief that links the Maillard reaction with texture.9 In a separate correlation analysis of one study, time to first crack showed no significant correlation with any attribute.9\n\n**What studies did not test.** No study opened for this entry separated the browning phase from drying in a sensory test. The 2024 study that roasted an extended Maillard profile measured titratable acidity, not flavour.1 Roast colour was a stronger predictor of flavour than roasting time.9\n\n**What roasters say.** According to a practitioner course, some roasters design their profiles to lengthen this phase.13 The same course doubts the benefit, because Maillard reactions are not limited to this phase.13 The 2024 study notes, citing a roasting reference, that an extended Maillard profile is thought to reduce sweetness and give flat or baked flavours.1 These are practitioner views, not findings.\n\n## Risks and defects\n\n- **Stretching the phase.** The extended Maillard profile of the 2024 study was designed to replicate a \"baked\" roast.1 Its sensory effect was not measured there; baked and underdeveloped roasts are covered under roast defects.\n- **Reading the probe as the bean.** The probe reads a mix of bean surface and hot air, specific to the machine, so phase temperatures cannot simply be compared between roasters.11 Colour change and first crack are judged on the beans themselves, by sight and by the first popping sounds.1\n- **Judging colour change by eye.** The start of the phase is the moment the beans visibly change colour1, so its measured length depends on who calls it.\n\n## Open questions\n\n- **Sensory effect of this phase alone.** No sensory study was found that varied colour change to first crack while holding drying, development and colour constant.9\n- **Exothermic onset.** Where in this phase the roast becomes exothermic is not agreed (see Contested).4,11\n- **Time courses on production roasters.** The sugar and acid time course here comes from a 25 g home roaster without recorded first crack3; matched chemistry and crack times from production drums were not found.\n- **Range of coffees.** The colour and acidity data come from three arabica coffees on one drum roaster.1,2\n\n## Key studies\n\n
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Anokye-Bempah et al., 2024 – Profiles and titratable acidity. Seven profiles on a 5 kg drum, with beans sampled every minute of 16 min roasts of three coffees. The paper reports the duration and mean rate of rise of the colour-change-to-first-crack phase for each profile; titratable acidity rose through it and always peaked at first crack.

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

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Anokye-Bempah et al., 2025 – A universal colour curve. Measures the colour of 663 ground samples from 39 roasts of three arabica coffees. All samples followed one curve in CIELAB space, and colour at colour change, first crack and second crack was about the same whatever the profile or origin.

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Scientific Reports 15, 24192 · doi:10.1038/s41598-025-06601-w

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Diviš et al., 2019 – Composition minute by minute. Follows sucrose, chlorogenic acid, organic acids and 5-hydroxymethylfurfural in a Brazilian arabica during a medium and a full city roast in a home roaster. Sucrose fell fastest in the middle of the roast and was almost gone at the end, while acetic, formic and lactic acids rose.

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Potravinarstvo Slovak Journal of Food Sciences 13(1), 344–350 · doi:10.5219/1062

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Wieland et al., 2012 – Watching the roast in real time. Follows volatile compounds in the exhaust of a 15–20 kg drum roaster by PTR-ToF-MS. Few aroma compounds appear before 500 s of a 894 s roast; many traces peak or level off at first crack.

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Analytical and Bioanalytical Chemistry 402(8), 2531–2543 · doi:10.1007/s00216-011-5401-9

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Münchow et al., 2020 – Colour versus timing. Pools eight sensory studies of washed arabica. At constant colour, development time affected flavour more than time to first crack, the span that contains drying and browning together; body was unaffected by either.

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Beverages 6(2), 29 · doi:10.3390/beverages6020029

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