{ "id": "roast-loss", "url": "https://coffearium.org/entries/roast-loss/", "license": "CC-BY-4.0", "title": "Roast loss", "summary": "The weight green coffee loses in the roaster, as a share of its starting weight – mostly water, plus carbon dioxide, other volatiles and chaff. A roast-degree index next to colour, and the step from green to roasted cost.", "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": "2026-10-14T00:00:00.000Z", "added": "2026-10-14T00:00:00.000Z", "brief": [ "Roast loss is the weight lost in roasting, as a percentage of the green-coffee weight. Sources give 15–22% and 14–23% for typical roasts.3,4", "Most of it is water. The rest is carbon dioxide, other volatiles, silverskin (chaff) and fine fragments.1,2,3", "Roast loss rises steadily through the roast and is higher in darker roasts.1,6", "Organic roast loss, calculated on dry matter, removes the effect of green-coffee moisture and is described as a more precise roast-degree index.1,5", "Because beans lose 15–22% of their weight, each roasted kilogram needs about 1.18–1.28 kg of green coffee (our calculation), which raises its cost.3" ], "quickFacts": [ { "label": "Definition", "value": "(green weight − roasted weight) ÷ green weight × 100" }, { "label": "Typical range", "value": "15–22% in one source; 14–23% in another" }, { "label": "Mostly", "value": "Water, from the green coffee and from reactions" }, { "label": "Silverskin", "value": "About 1 g per 100 g green coffee" }, { "label": "Fast vs slow, same colour", "value": "15.38% vs 15.86% (one fluid-bed study)" }, { "label": "Organic roast loss", "value": "Roast loss on a dry-matter basis" }, { "label": "Cost", "value": "Roasted cost = green cost ÷ (1 − roast loss)" } ], "aka": [ "Roasting loss", "Weight loss in roasting", "Shrinkage" ], "linkTerms": [ "roast loss", "roasting loss", "weight loss in roasting", "mass loss in roasting", "roast shrinkage", "roast yield" ], "related": [ "roasting", "roast-degree-and-colour", "degassing", "roast-profile", "development-time", "moisture-and-water-activity", "green-coffee-composition", "decaffeination", "freshness-and-storage", "cupping" ], "contested": [ "Roast loss or colour as the control parameter: a roasting textbook chapter and a doctoral thesis describe roast loss and organic roast loss as indicators of roast degree, with organic roast loss correlating well with lightness1,5; the SCA allows dry-matter loss for cupping roasts only once its correlation with colour or spectrometry has been established8; a chemistry chapter holds that weight loss and colour together are not sufficient to characterise roasted-coffee quality.11", "Share of the roast loss explained by gas and chaff: in the fluid-bed study, the measured water, carbon dioxide and silverskin add up to 13.3 g (fast) and 13.0 g (slow) against a weighed roast loss of 15.38 g and 15.86 g per 100 g; the authors, taking the spread of their data into account, give about 96% and 93%, and attribute the rest to abrasion, other gases and measurement uncertainty2; on the mean values of their table alone, the shares are about 86% and 82% (our calculation)." ], "corrections": [], "sources": [ { "id": "s1", "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 loss of pure organic dry matter would provide more precise information on roast degree because it takes the varying loss of water into account.", "accessed": "2026-10-14T00:00:00.000Z" }, { "id": "s2", "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": "Material from abrasion, for example, tippings, and evolving gases other than CO2 and water vapor also contribute to the total roast loss.", "accessed": "2026-10-14T00:00:00.000Z" }, { "id": "s3", "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": "During the roasting process, the beans lose between 15 and 22% of their weight, of which most is water as it ends up as a rather dry product with between 1 and 2.5% moisture", "accessed": "2026-10-14T00:00:00.000Z" }, { "id": "s4", "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": "During the roasting process, weight loss usually varies between 14-23% depending on the botanical origin, green coffee moisture, storage conditions, and the roasting method.", "accessed": "2026-10-14T00:00:00.000Z" }, { "id": "s5", "title": "Investigations on the Hot Air Roasting of Coffee Beans (Diss. ETH No. 13620)", "authors": "Schenker, S.", "year": 2000, "publisher": "ETH Zürich (doctoral thesis)", "url": "https://library.sweetmarias.com/wp-content/uploads/2020/08/roasting_hot_air_doctorate.pdf", "tier": "B", "quote": "The overall weight difference between the green coffee batch and the roasted batch immediately after roasting and cooling was defined as roast loss (RL):", "accessed": "2026-10-14T00:00:00.000Z" }, { "id": "s6", "title": "Physicochemical characteristics of Ethiopian Coffea arabica cv. Heirloom coffee extracts with various roasting conditions", "authors": "Kim, I.; Jung, S.; Kim, E.; Lee, J.-W.; Kim, C.-Y.; Ha, J.-H.; Jeong, Y.", "year": 2021, "publisher": "Food Science and Biotechnology 30(2), 235–244", "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC7914306", "doi": "10.1007/s10068-020-00865-w", "tier": "A", "quote": "The weight loss of the coffee beans was increased as the roasting degree increased.", "accessed": "2026-10-14T00:00:00.000Z" }, { "id": "s7", "title": "A Kinetics and Modeling Study of Coffee Roasting Under Isothermal Conditions", "authors": "Wang, X.; Lim, L.-T.", "year": 2014, "publisher": "Food and Bioprocess Technology 7, 621–632", "url": "https://link.springer.com/doi/10.1007/s11947-013-1159-8", "doi": "10.1007/s11947-013-1159-8", "tier": "A", "quote": "The first-to-second stage transition for L* value and roast loss occurred at light-medium roast.", "abstractOnly": true, "accessed": "2026-10-14T00:00:00.000Z" }, { "id": "s8", "title": "SCA Standard 102-2024 Coffee Value Assessment: Sample Preparation and Tasting Mechanics", "authors": "Specialty Coffee Association", "year": 2024, "publisher": "Specialty Coffee Association", "url": "https://sca.coffee/s/AW_SCA-102_Sample-Preparation_281024_Secured.pdf", "tier": "A", "quote": "Alternative methods for roast level control, such as dry matter loss, or volume increase of the coffee bean, may be used if correlations with colorimetry or spectrometry have been established.", "accessed": "2026-10-14T00:00:00.000Z" }, { "id": "s9", "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 the roast-level methods it permits; B otherwise.", "quote": "The roast level may be controlled through four alternative methods: colorimetry (e.g., CIELAB or Agtron/SCA Roast Color Classification System), infrared spectrometry (e.g., Agtron device), dry matter loss, or volume increase of the coffee bean.", "accessed": "2026-10-14T00:00:00.000Z" }, { "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": "Roast degree can be defined in various ways, including bean weight loss, colour, or selected chemical indicators", "accessed": "2026-10-14T00:00:00.000Z" }, { "id": "s11", "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": "It is widely accepted that characterizing the quality of roasted coffee only by means of weight loss and/or roast color is not sufficient, since these attributes do not make a statement about the individually obtained aroma profiles.", "accessed": "2026-10-14T00:00:00.000Z" }, { "id": "s12", "title": "Decaffeination – Process and Quality", "authors": "Pietsch, A.", "year": 2017, "publisher": "In: Folmer, B. (ed.), The Craft and Science of Coffee, Academic Press, ch. 10, pp. 225–243", "url": "https://doi.org/10.1016/B978-0-12-803520-7.00010-4", "doi": "10.1016/B978-0-12-803520-7.00010-4", "tier": "B", "quote": "Suitable target roasting color can be different from non-decaffeinated beans and sometimes mass loss is the better control parameter.", "accessed": "2026-10-14T00:00:00.000Z" } ], "markdown": "## What roast loss is\n\nGreen coffee goes into the roaster heavier than it comes out. Roast loss is that difference, given as a percentage of the green-coffee weight.1,5 For example, 10 kg of green coffee that leaves the roaster at 8.4 kg has a roast loss of 16%.\n\nOne multi-study paper puts typical roast loss at 15–22%;3 a study of roast colour cites 14–23%.4 The value depends on the green coffee, its moisture, the roasting conditions and the final roast degree.1,4 The roasting textbook chapter used here stresses that roast loss is always specific to the product.1\n\nThe roasted weight that remains is sometimes called the roast yield. With a roast loss of 16%, the yield is 84% (our calculation).\n\n## What the beans lose\n\nMost of the lost weight is water. Roasted beans end with only 1–2.5% moisture (basis not stated).3 The rest of the loss comes from several sources:1,2\n\n- **Water from the green coffee.** It evaporates first; the highest rate of roast loss is usually early in the roast.1\n- **Water formed by reactions.** Chemical reactions in the bean produce water as well, which also evaporates.1,2\n- **Carbon dioxide and other volatiles.** Reactions turn part of the dry matter into gases and volatile compounds.1,2\n- **Silverskin.** The thin skin left on green coffee comes off as the bean swells and is carried away as chaff. It accounts for about 1% of the weight.1,2\n- **Dust and fragments.** Abrasion and broken pieces are carried off with the air.1,2\n\nA Swiss laboratory study measured these parts directly. It roasted 100 g batches of green coffee in a fluid bed, fast and slow, to the same colour.2 It recorded water vapour and carbon dioxide in the exhaust air throughout the roast, estimated the chaff from the skins of five beans, and weighed the beans.2\n\n
\n
\n
    \n
  1. Water. 10.2 g (fast) and 11.4 g (slow) evaporated during roasting, plus 1.6 g and 0.1 g estimated for cooling; in the fast roast, the thin line marks the end of roasting.2
    2. \n
  2. Carbon dioxide in the roaster. 0.4 g (fast) and 0.50 g (slow) during roasting, plus 0.1 g and 0.0 g estimated for cooling.2
    3. \n
  3. Silverskin. 1.0 g in both roasts.2
    4. \n
  4. Not accounted for. Weighed roast loss minus the measured sum of 13.3 g (fast) and 13.0 g (slow): 2.08 g and 2.86 g (our calculation). The authors name abrasion, other gases and measurement uncertainty.2
    5. \n
  5. Carbon dioxide in storage. 0.99 g (fast) and 0.83 g (slow) in the 63 days after roasting – lost later, not part of the roast loss. With the gas from roasting and cooling, the totals are 1.49 g and 1.33 g.2
    6. \n
  6. Weighed roast loss. 15.38% (fast, 170 s at 260 °C air) and 15.86% (slow, 720 s at 228 °C air), both at L* 22–23.2
    7. \n
\n

Formulas

\n\n
Where 100 g of green coffee loses its weight in a fast and a slow roast to the same colour in a laboratory fluid bed; drawn to scale. Values from Table 2 of the study; the “not accounted for” part is our calculation.2
\n
\n\nWater dominates in both roasts. Carbon dioxide in the roaster is small – about half a gram per 100 g – and more of it escapes later, during storage.2 That later gas is the subject of degassing.\n\n## Roast loss and roast degree\n\nRoast loss increases steadily during roasting, and dark roasts lose more weight than light ones.1 In a 2021 study of an Ethiopian arabica, the beans lost about 12% at light-medium and medium roast, about 16% at moderately dark and about 20% at very dark.6 Researchers therefore list weight loss as one way to define roast degree, next to colour and chemical indicators.10\n\n
\n
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Roast loss reported in the sources: two literature ranges3,4, an Ethiopian arabica from light-medium to very dark6, arabica and robusta at the same three roast intensities4, and a fast and a slow fluid-bed roast to the same colour.2
\n
\n\nRoast loss has a weakness as an index. It reflects how much water the green coffee brought in.1 According to the textbook chapter, beans with more moisture lose more water and end at a similar final moisture, so their roast loss is higher.1 Two batches roasted to the same colour can therefore differ in roast loss.1\n\n**Organic roast loss** corrects for this. It counts only the dry matter lost, so differences in water content drop out.1,5 According to the textbook chapter, it correlates well with lightness from colour measurement.1 It needs moisture measurements of both green and roasted coffee.1,5\n\nColour is the other main index of roast degree (see Roast degree and colour).10 The SCA allows dry-matter loss as an alternative for cupping roasts, once it has been correlated with colour or spectrometry.8,9\n\n## Measuring roast loss\n\nRoast loss is measured by weighing. The weight of the green batch and of the roasted batch is all you need.1,5 Research protocols state when and what they weigh:\n\n1. **Weigh the green coffee** before charging it.5\n2. **Weigh the roasted coffee after cooling.** A doctoral study defined roast loss from the roasted batch weighed immediately after roasting and cooling.5 Cooling still removes weight: in the fluid-bed study, an estimated 1.7 g per 100 g left the fast roast during cooling.2\n3. **Weigh at a fixed time.** Roasted beans go on losing carbon dioxide in storage, 0.83–0.99 g per 100 g over 63 days in one study.2\n4. **Calculate** RL = (green weight − roasted weight) ÷ green weight × 100.1,6\n\nLaboratory studies weigh whole batches2 or a counted sample: one study weighed 100 beans before and after roasting.4 Water quenching can distort the result. Too much quench water is absorbed by the beans and raises their final moisture,1 which lowers the measured roast loss.\n\n## Roast loss and the cost of roasted coffee\n\nBecause the beans lose 15–22% of their weight,3 a kilogram of roasted coffee needs more than a kilogram of green coffee. The green cost is spread over less product, so the cost per roasted kilogram is the green cost divided by (1 − roast loss) (our calculation).\n\n**An example (our calculation, illustrative prices).** Green coffee costs CHF 10.00 per kg landed. At 15% roast loss, the roasted coffee costs CHF 11.76 per kg; at 18%, CHF 12.20; at 20%, CHF 12.50. A 60 kg bag at 18% yields 49.2 kg of roasted coffee. Adding the percentage instead (CHF 10.00 × 1.18 = CHF 11.80) understates the cost.\n\nIn the calculator below, enter an origin price, shipping and import costs, and your roast loss. You get the landed cost per kilogram of green coffee, the cost per roasted kilogram and the cost per cup.\n\n
\n
\n
Our calculator; the example values are for illustration, not market quotes. Its default roast loss of 18% lies within the 15–22% reported in a multi-study paper.3
\n
\n\n\n\n## Reference values\n\n| Parameter | Value reported | Source |\n|---|---|---|\n| Typical roast loss (literature) | 15–22%; 14–23% | Münchow et al.3, Bicho et al.4 |\n| Moisture after roasting (basis not stated) | 1–2.5% | Münchow et al.3 |\n| Ethiopian arabica (cv. Heirloom) by roast degree | Light-medium and medium ≈12%; moderately dark ≈16%; very dark ≈20% | Kim et al.6 |\n| Arabica, three roast intensities (200–240 °C, 5–12 min; 100 beans weighed) | 10.5 ± 0.2, 13.4 ± 0.1, 19.4 ± 0.4%; ground L\\* 49.8, 41.9, 37.4 | Bicho et al.4 |\n| Robusta, same three roasts | 10.1 ± 0.4, 12.5 ± 0.2, 16.7 ± 0.4%; ground L\\* 52.5, 45.7, 39.8 | Bicho et al.4 |\n| Fluid bed, 100 g batches, L\\* 22–23 (green moisture 8.3 g/100 g, wb) | Fast (170 s, 260 °C air) 15.38 ± 0.05%; slow (720 s, 228 °C air) 15.86 ± 0.02% | Geiger et al.2 |\n| Water evaporated during roasting, per 100 g green | 10.2 ± 1.2 g (fast); 11.4 ± 1.4 g (slow) | Geiger et al.2 |\n| Share of evaporated water formed by reactions | 41% (fast); 36% (slow) | Geiger et al.2 |\n| Cooling loss, calculated, per 100 g green | Water 1.6 g, CO₂ 0.1 g (fast); water 0.1 g, CO₂ 0.0 g (slow) | Geiger et al.2 |\n| Silverskin | 1.0 g per 100 g green (both roasts); about 1% weight loss | Geiger et al.2, Schenker & Rothgeb1 |\n| CO₂ in the roaster, per 100 g green | 0.4 g (fast); 0.50 g (slow) | Geiger et al.2 |\n| CO₂ in 63 days of storage, per 100 g green | 0.99 g (fast); 0.83 g (slow) | Geiger et al.2 |\n| CO₂ in total (roasting, cooling and 63 days) | 1.49 g (fast, including 0.1 g estimated for cooling); 1.33 g (slow) per 100 g green (sum of the study’s values) | Geiger et al.2 |\n| Roast loss explained by gas and chaff | About 96% (fast) and 93% (slow), taking the data’s spread into account | Geiger et al.2 |\n\n## The mass balance in detail\n\nThe fluid-bed study gives a full mass balance of roast loss. Its fast and slow roasts ended at almost the same weighed loss, but by different routes.2 The slow roast evaporated more water while in the roaster; the fast roast lost more during the estimated cooling step.2 Reaction water made up 41% of the evaporated water in the fast roast and 36% in the slow one.2 After about 300 s of the slow roast, the evaporation of the original water had become almost negligible, and reaction water was formed and evaporated at the same rate.2\n\nThe balance does not close. Water, carbon dioxide and chaff sum to 13.3 g (fast) and 13.0 g (slow) per 100 g, against 15.38 g and 15.86 g weighed.2 The authors, allowing for the spread of their values, state that about 96% and 93% of the roast loss was explained.2 On the mean values alone, the shares are about 86% and 82% (our calculation). Abrasion material, gases other than carbon dioxide and water vapour, and measurement uncertainty are named for the rest.2\n\nThe study used a laboratory roaster with 100 g batches, a high air-to-bean ratio and green coffee at 8.3 g/100 g moisture (wet basis).2 The authors call for the measurements to be extended to other coffees and roasting conditions; production drum roasters, wetter green coffee and longer profiles may give other numbers.2 The pattern – mostly water, a small share of gas, about 1 g of chaff – is consistent with the textbook description.1\n\n## Organic roast loss\n\nOrganic roast loss (ORL) is the loss of dry matter during roasting:1,5\n\nORL = 100 − (100 − RL) × dmroast ÷ dmgreen\n\nHere RL is the roast loss in %, and dmgreen and dmroast are the dry matter of green and roasted coffee in g per 100 g (wet basis).1,5 Written this way, ORL is the dry matter lost as a percentage of the dry matter in the green coffee, not of its total weight (our reading of the formula). Dry matter is found by drying a sample: the fluid-bed study ground the roasted beans finely and dried them at 103 °C for 5 h.2 The doctoral study used oven or infrared drying for roasted coffee and a two-step procedure for green coffee.5\n\n**Worked example (our calculation, illustrative values).** Green coffee at 11.0% moisture, wet basis (dry matter 89.0) is roasted with 16.0% roast loss to 2.0% moisture (dry matter 98.0). ORL = 100 − 84.0 × 98.0 ÷ 89.0 = 7.5%. A second lot at 12.0% moisture, roasted to the same ORL and the same final moisture, shows a roast loss of 16.9%. One point more green moisture adds almost one point of roast loss, with no change in dry-matter loss.\n\nBy this definition, reaction water counts as dry-matter loss, because chemical reactions form it from the dry matter (our reading of the definition).1,2 According to the textbook chapter, loss of organic matter starts later in the roast than dehydration.1\n\n## Speed, moisture and coffee\n\n**Roast speed.** At the same colour, the slow fluid-bed roast lost slightly more weight than the fast one: 15.86% against 15.38%.2 According to a doctoral thesis from the same laboratory, earlier roasts to a similar colour showed the same direction.5 Both come from one laboratory and one roaster type; no study opened for this entry tested the difference on production drum roasters.\n\n**Roast course.** In an isothermal kinetics study, roast loss and L\\* each followed two stages, with the change at light-medium roast.7 Roast loss followed zero-order kinetics, with a separate activation energy for each stage.7\n\n**Moisture.** Wetter green coffee gives a higher roast loss at the same final moisture.1 The colour study lists green-coffee moisture, storage conditions, botanical origin and roasting method among the factors behind the range.4\n\n**Species.** In a 2012 study, arabica and robusta roasted at the same three intensities lost 10.5–19.4% and 10.1–16.7% respectively.4 The authors attribute the higher loss of arabica in part to more volatiles.4 At each intensity the ground arabica was also darker than the robusta.4\n\n
\n
\n
Lightness of the ground coffee against roast loss for arabica and robusta roasted at the same three intensities (200–240 °C, 5–12 min), measured under illuminant D65.4
\n
\n\n**Decaffeinated coffee.** Decaffeination changes the beans’ structure and composition. A suitable target colour can differ from that of regular coffee, and mass loss is sometimes the better control parameter.12\n\n## Uses and limits\n\n- **Batch consistency.** As long as the quality and moisture of the green coffee stay constant, roast loss can serve as an indicator of roast degree.1 When moisture varies, organic roast loss is the more precise index.1,5\n- **Cupping roasts.** The SCA allows dry-matter loss to control the roast level of cupping samples once its correlation with colorimetry or spectrometry has been established; it is researching these correlations.8,9\n- **Flavour.** Roast loss does not describe flavour on its own. A chemistry chapter holds that weight loss and colour together cannot characterise roasted-coffee quality, because they say nothing about the aroma profile.11 In two sensory studies, colour predicted flavour better than roasting time.3\n- **Costing.** Roast loss enters every cost calculation from green to roasted coffee (see the calculator above). Because roast loss is always specific to the product,1 a value measured on the roaster’s own batches fits a costing better than a literature range.\n\n## Open questions\n\n- **Production roasters.** The only full mass balance opened for this entry comes from a 100 g laboratory fluid bed.2 No study opened for this entry measured the same breakdown in a production drum roaster.\n- **The missing share.** Up to about one-sixth of the weighed loss was not covered by the gas and chaff measurements on mean values (our calculation).2 How much of it is abrasion, other gases or measurement uncertainty is not established.\n- **Organic roast loss and flavour.** The correlation with lightness is described in a textbook chapter;1 no study opened for this entry tested organic roast loss against sensory data.\n- **Speed at production scale.** Whether slow roasts lose more weight at equal colour beyond the one laboratory remains untested in the sources opened.2,5\n\n## Key studies\n\n
\n

Geiger et al., 2005 – Carbon dioxide and water during roasting. Measures water vapour and carbon dioxide in the exhaust of a laboratory fluid bed for a fast and a slow roast to the same colour, and weighs chaff and beans. Water dominates the loss; gas measurements and chaff explain most of the weighed roast loss, and more carbon dioxide leaves later, in storage.

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Journal of Food Science 70(2), E124–E130 · doi:10.1111/j.1365-2621.2005.tb07084.x

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Bicho et al., 2012 – Colour parameters in roasting. Roasts arabica and robusta together at three intensities and records mass loss of 100 beans with colour, whole and ground. Arabica lost more weight than robusta at each intensity, and lightness fell steadily with roasting.

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Ciência e Tecnologia de Alimentos 32(3), 436–442 · doi:10.1590/S0101-20612012005000068

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Kim et al., 2021 – Ethiopian arabica at four roast degrees. Roasts one Ethiopian arabica from light-medium to very dark and measures weight loss, moisture, colour and extract chemistry. Weight loss rose with roast degree, from about 12% to about 20%.

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Food Science and Biotechnology 30(2), 235–244 · doi:10.1007/s10068-020-00865-w

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Wang and Lim, 2014 – Roasting kinetics. Roasts arabica isothermally at four temperatures and models lightness, roast loss, residual carbon dioxide and volatiles. Lightness and roast loss each changed in two stages, with the transition at light-medium roast.

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Food and Bioprocess Technology 7, 621–632 · doi:10.1007/s11947-013-1159-8

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" }