{ "id": "processing-defects", "url": "https://coffearium.org/entries/processing-defects/", "license": "CC-BY-4.0", "title": "Green coffee defects and their causes", "summary": "Where each physical defect in green coffee comes from – the field, the wet mill, drying, the dry mill or storage – what it looks like, how it can change the cup, and how producers and mills prevent it.", "domain": "post-harvest-processing", "kind": "Concept", "stage": "process", "topics": [], "topicSections": {}, "lang": "en", "status": "verified", "reviewer": "Coffearium verification pass", "lastVerified": "2026-10-21T00:00:00.000Z", "updated": "2026-10-21T00:00:00.000Z", "added": "2026-10-21T00:00:00.000Z", "brief": [ "Most green coffee defects can be traced to one or more stages – the field, harvest and wet mill, drying, the dry mill or storage.9,2,5", "Black beans are linked to overripe or fallen fruit left to ferment and dried badly; in the cup they give bitter, acrid and carbonous flavours.6,2,7", "Stinkers look normal or nearly so but smell putrid when cut; long fermentation, unclean water and badly cleaned tanks or pulpers cause them.2,3,14", "Broken beans come mostly from hulling over-dried coffee or from badly set machines; nipped beans come from a badly adjusted pulper.2,3,5", "Black and sour defects carried the highest ochratoxin A levels in lower-grade coffee; sorted-out defects should not be blended back unless testing shows them acceptable.1" ], "quickFacts": [ { "label": "Cause classes", "value": "Field · harvest and wet mill · drying · dry mill · storage and transport" }, { "label": "Highest ochratoxin A", "value": "Black and sour defects, in lower-grade coffee (Codex)" }, { "label": "Breakage at hulling", "value": "Coffee hulled too dry; badly set hullers" }, { "label": "Stinker", "value": "Looks normal or nearly so; putrid odour when cut" }, { "label": "Quakers", "value": "Pale after roasting; from immature seeds; 7 in 65 beans affected the cup in one study" } ], "aka": [ "Coffee defects", "Green coffee defects", "Defective beans", "Causes of coffee defects" ], "linkTerms": [ "green coffee defect", "green coffee defects", "defective bean", "defective beans", "black bean", "black beans", "sour bean", "sour beans", "foxy bean", "foxy beans", "triage" ], "related": [ "green-coffee-grading", "grading-and-sorting", "harvesting-and-sorting", "pulping", "fermentation", "drying", "hulling-and-dry-milling", "coffee-berry-borer", "ochratoxin-a", "green-coffee-storage", "roast-defects", "moisture-and-water-activity" ], "contested": [ "Origin of black beans: an FAO manual attributes them to prolonged fermentation of cherries picked from the ground, followed by poor drying with intermittent wetting2; a 2008 study says they most commonly come from over-ripened cherries lying on the soil, but also from carbohydrate deficiency caused by poor agricultural practices6; a Cenicafé guide describes green beans that ferment within the coffee mass and turn black.7 A Brazilian guide puts the cause in long contact with microorganisms and moisture.5 The sources agree on fermentation and moisture but not on how much starts on the tree.", "Field or process for sour beans: a 2008 study names water shortage during fruit development as well as abnormal fermentation6, and a Brazilian guide says the fermentation may begin while the fruit is still on the plant5; the Brazilian regulation defines the sour bean by its brown colour, which it attributes to fermentation processes.4", "How well defect counts predict the cup: in a Korean study, the share of defective beans rose as sensory scores fell across NY grades17, and quakers lowered the sensory quality of natural coffees only from 7 in a cup of 65 beans.10 An SCA article states that research linking physical defects to negative flavours is insufficient, and that some of the strongest cup defects are not visible.15" ], "corrections": [ { "date": "2026-10-21T00:00:00.000Z", "change": "Removed the 11% moisture threshold for breakage at hulling (quick facts and defect table).", "reason": "It rested only on the EPAMIG guide, now rated Tier B (a single Tier B source cannot carry a number)." }, { "date": "2026-10-21T00:00:00.000Z", "change": "The SCA weighting of three partial blacks to one full black is now also cited to the SCA Coffee Value Assessment (new source 18).", "reason": "The number rested only on an SCA magazine article (Tier B); the CVA defect-equivalents table (Tier A for what it specifies) gives the same weight." }, { "date": "2026-10-21T00:00:00.000Z", "change": "Contested item on sour beans corrected – the Brazilian regulation attributes the brown colour to fermentation processes; the body now says so.", "reason": "MAPA IN 8/2003, item 3.5, defines the ardido bean with a cause; the draft said it defined it by colour only." }, { "date": "2026-10-21T00:00:00.000Z", "change": "The Cenicafé 2016 estimate now reads “more than 80% of bean defects, among them vinegar, discoloured, soft and mouldy beans”.", "reason": "The paper estimates the share of all bean defects that come from processing and drying, not the share of each named defect." }, { "date": "2026-10-21T00:00:00.000Z", "change": "Causes of faded and aged beans corrected to uneven or too-hot drying (above 55 °C) and poor storage; “delays in drying” removed.", "reason": "Cenicafé Avances Técnicos 461 names these causes for the reposado defect; delays in drying appear there only under mouldy beans." }, { "date": "2026-10-21T00:00:00.000Z", "change": "Crushed beans – visual cue added (flat bean with the median furrow laid open) and FAO 2000 added as a source for the cause; cause-matrix figure updated.", "reason": "The FAO manual describes the crushed bean; the draft said it was not described." }, { "date": "2026-10-21T00:00:00.000Z", "change": "Smaller precision fixes – the 20% share of defective Brazilian production is given as stated by the 2008 study, not measured by it; Casas et al. roasted-bean compounds “dominated by” volatiles, acids and sugars; the Korean study no longer called Brazilian; the borer sentence cites the field origin to the sources that state it; the Codex no-blend-back rule keeps its testing exception.", "reason": "Wording was stronger or more specific than the sources." } ], "sources": [ { "id": "s1", "title": "Code of Practice for the Prevention and Reduction of Ochratoxin A Contamination in Coffee (CAC/RCP 69-2009)", "authors": "Codex Alimentarius Commission (FAO/WHO)", "year": 2009, "publisher": "Codex Alimentarius", "url": "https://www.fao.org/input/download/standards/11250/CXP_069e.pdf", "tier": "A", "quote": "Remove defects from main-crop production, discarding or screening them before their inclusion into the food chain.", "accessed": "2026-10-21T00:00:00.000Z" }, { "id": "s2", "title": "Post Harvest Handling and Processing of Coffee in African Countries, 3.0 Post Harvest Handling and Processing of Green Coffee in African Countries", "authors": "Mutua, J.", "year": 2000, "publisher": "FAO", "url": "https://www.fao.org/4/X6939E/X6939e03.htm", "tier": "A", "quote": "It has now been established that stinkers are caused either by excessively long fermentation or the use of unclean water.", "accessed": "2026-10-21T00:00:00.000Z" }, { "id": "s3", "title": "Arabica coffee manual for Lao-PDR", "authors": "Winston, E.; Op de Laak, J.; Marsh, T.; Lempke, H.; Chapman, K.", "year": 2005, "publisher": "FAO Regional Office for Asia and the Pacific, Bangkok", "url": "https://www.fao.org/4/ae939e/ae939e08.htm", "tier": "A", "quote": "Nipped beans causing stinker beans", "accessed": "2026-10-21T00:00:00.000Z" }, { "id": "s4", "title": "Instrução Normativa nº 8, de 11 de junho de 2003 — Regulamento Técnico de Identidade e de Qualidade para a Classificação do Café Beneficiado Grão Cru", "authors": "Ministério da Agricultura, Pecuária e Abastecimento (MAPA), Brazil", "year": 2003, "publisher": "MAPA (copy hosted by IDR-Paraná, Paraná state government)", "url": "https://idrparana.pr.gov.br/sites/iapar/arquivos_restritos/files/documento/2020-07/cafebenef008_03.pdf", "tier": "A", "tierNote": "Official regulation (Diário Oficial text, signed by the Minister of Agriculture); A for what it requires", "quote": "grão danificado pela broca do café, apresentando um ou mais orifícios limpos ou sujos", "accessed": "2026-10-21T00:00:00.000Z" }, { "id": "s5", "title": "Origem dos defeitos e procedimentos para classificação por tipo de café commodity", "authors": "Nadaleti, D. H. S.; Moreira, P. C.; Maia, P. L.; Carvalho, G. R.; Malta, M. R.; Botelho, C. E.; Matos, C. S. M.", "year": 2020, "publisher": "EPAMIG Sul (Empresa de Pesquisa Agropecuária de Minas Gerais), Lavras", "url": "https://livrariaepamig.com.br/wp-content/uploads/2023/02/Origem-dos-defeitos-e-procedimentos-para-classificacao-por-tipo-de-cafe-commodity.pdf", "tier": "B", "tierNote": "Technical guide of a Brazilian state agricultural research company (Minas Gerais), with no series, ISSN or stated review; not formally Tier A, so B (Alcide, 21 Oct 2026). Never carries a number alone. Imprint reads “fevereiro/20”", "quote": "perfuração pela broca-do-café e presença de fungos nos orifícios", "accessed": "2026-10-21T00:00:00.000Z" }, { "id": "s6", "title": "Volatile compounds as potential defective coffee beans’ markers", "authors": "Toci, A. T.; Farah, A.", "year": 2008, "publisher": "Food Chemistry 108(3), 1133–1141", "url": "https://pages.uoregon.edu/chendon/coffee_literature/old_literature/2008%20Food%20Chem.,%20Volatiles%20in%20defective%20coffee.pdf", "doi": "10.1016/j.foodchem.2007.11.064", "tier": "A", "quote": "Immature beans originate mainly from immature fruits and are known to increase beverage astringency", "accessed": "2026-10-21T00:00:00.000Z" }, { "id": "s7", "title": "Cómo garantizar la buena calidad de la bebida del café y evitar los defectos (Avances Técnicos 284)", "authors": "Puerta-Quintero, G. I.", "year": 2001, "publisher": "Cenicafé", "url": "https://biblioteca.cenicafe.org/bitstream/10778/562/1/avt0284.pdf", "tier": "A", "quote": "Negros: producen los defectos acre y carbonoso.", "accessed": "2026-10-21T00:00:00.000Z" }, { "id": "s8", "title": "Buenas prácticas para la prevención de los defectos de la calidad del café: fermento, reposado, fenólico y mohoso (Avances Técnicos 461)", "authors": "Puerta-Quintero, G. I.", "year": 2015, "publisher": "Cenicafé", "url": "https://www.cenicafe.org/es/publications/avt0461.pdf", "tier": "A", "quote": "Los granos defectuosos se pueden originar desde el cultivo, principalmente por plagas como la broca del cafeto.", "accessed": "2026-10-21T00:00:00.000Z" }, { "id": "s9", "title": "Calidad física del café de varias regiones de Colombia según altitud, suelos y buenas prácticas de beneficio", "authors": "Puerta-Quintero, G. I.", "year": 2016, "publisher": "Revista Cenicafé 67(1), 7–40", "url": "https://www.cenicafe.org/es/publications/1.Calidad.pdf", "tier": "A", "quote": "Se midió la calidad física de 162 muestras de café con trazabilidad registrada de origen y procesos de la finca", "accessed": "2026-10-21T00:00:00.000Z" }, { "id": "s10", "title": "Impacts of quaker beans over sensory characteristics and volatile composition of specialty natural coffees", "authors": "Rabelo, M. H. S.; Borém, F. M.; Lima, R. R.; Alves, A. P. C.; Pinheiro, A. C. M.; Ribeiro, D. E.; Santos, C. M.; Pereira, R. G. F. A.", "year": 2021, "publisher": "Food Chemistry 342, 128304", "url": "https://educapes.capes.gov.br/handle/capes/1162122", "doi": "10.1016/j.foodchem.2020.128304", "tier": "A", "quote": "Therefore, the color and sensory characteristics of Quaker are a consequence of the chemical composition of an immature bean.", "abstractOnly": true, "accessed": "2026-10-21T00:00:00.000Z" }, { "id": "s11", "title": "Identification of biochemical features of defective Coffea arabica L. beans", "authors": "Casas, M. I.; Vaughan, M. J.; Bonello, P.; McSpadden Gardener, B.; Grotewold, E.; Alonso, A. P.", "year": 2017, "publisher": "Food Research International 95, 59–67", "url": "https://agris.fao.org/search/ar/records/65de48f70f3e94b9e5ccf9f7", "doi": "10.1016/j.foodres.2017.02.015", "tier": "A", "quote": "The presence of defective beans during processing and roasting contribute to off flavors and reduce overall cup quality", "abstractOnly": true, "accessed": "2026-10-21T00:00:00.000Z" }, { "id": "s12", "title": "Physicochemical Characteristics of Green Coffee: Comparison of Graded and Defective Beans", "authors": "Ramalakshmi, K.; Kubra, I. R.; Rao, L. J. M.", "year": 2007, "publisher": "Journal of Food Science 72(5), S333–S337", "url": "https://searchworks.jioinstitute.edu.in/articles/asx__25490074", "doi": "10.1111/j.1750-3841.2007.00379.x", "tier": "A", "quote": "Defective (triage) coffee beans are beans rejected after separating the graded ones according to the size and color.", "abstractOnly": true, "accessed": "2026-10-21T00:00:00.000Z" }, { "id": "s13", "title": "The Harvest and Post-Harvest Management Practices' Impact on Coffee Quality", "authors": "Haile, M.; Kang, W. H.", "year": 2019, "publisher": "In: Castanheira, D. T. (ed.), Coffee – Production and Research, IntechOpen", "url": "https://www.intechopen.com/chapters/70151", "doi": "10.5772/intechopen.89224", "tier": "B", "tierNote": "IntechOpen edited-book chapter (labelled “peer-reviewed chapter” by the publisher); B under the house rule for IntechOpen chapters", "quote": "Overdried fruits have brittle characteristics and produce many defective (broken) during hulling.", "accessed": "2026-10-21T00:00:00.000Z" }, { "id": "s14", "title": "Coffee Wet Mill Processing Guide", "authors": "TechnoServe", "publisher": "TechnoServe", "url": "https://www.technoserve.org/wp-content/uploads/2022/03/TechnoServe-Wet-Mill-Processing-Guide.pdf", "tier": "B", "tierNote": "Non-profit development organisation (NGO); B", "quote": "nipping the parchment off the beans resulting in naked/white beans", "accessed": "2026-10-21T00:00:00.000Z" }, { "id": "s15", "title": "Grounding Green Grading in Sensory Science: Research to Understand Physical Coffee Defects", "authors": "Carmichael, L.", "publisher": "Specialty Coffee Association, 25 Magazine, Issue 24", "url": "https://sca.coffee/sca-news/25/issue-24-grounding-green-grading", "tier": "B", "quote": "there is insufficient research actually linking these physical defects to negative flavors", "accessed": "2026-10-21T00:00:00.000Z" }, { "id": "s16", "title": "Calidad del café (cartilla de calidad física y sensorial)", "authors": "Servicio de Extensión, Comité Departamental de Cafeteros de Caldas", "publisher": "Comité Departamental de Cafeteros de Caldas (copy in the Cenicafé library)", "url": "https://biblioteca.cenicafe.org/bitstream/10778/1033/1/Calidad%20caf%C3%A9.pdf", "tier": "B", "tierNote": "Extension leaflet of a departmental coffee growers' committee; year not printed", "quote": "Ataque de insectos como el gorgojo y la broca", "accessed": "2026-10-21T00:00:00.000Z" }, { "id": "s17", "title": "Contents of Defective Beans and Cup Quality in Relation to the Grade and Processing Methods of Green Coffee", "authors": "Yoon, H.-H.; Choi, Y.-M.", "year": 2009, "publisher": "Korean Journal of Food and Cookery Science 25(6), 703–711", "url": "https://koreascience.kr/article/JAKO200916955021418.do", "tier": "A", "quote": "the percentage of defective beans increased as sensory characteristics decreased", "abstractOnly": true, "accessed": "2026-10-21T00:00:00.000Z" }, { "id": "s18", "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 what the CVA itself specifies (physical assessment procedure, defect equivalents); B for its explanations", "quote": "The full defect equivalents of each category (category 1 and category 2) are added up and reported by category.", "accessed": "2026-10-21T00:00:00.000Z" } ], "markdown": "## What a defect is\n\nA defect is an unwanted particle in green coffee: a defective bean or piece of bean, fruit tissue or foreign matter.1 Graders find defects by eye, on a sample of the lot.18 A lot is a batch of coffee from one origin and process, traded as a unit. Brazil’s grading regulation defines most defects by how they look. A black bean is opaque black; an insect-damaged bean has one or more holes.4\n\nDefects are common. A 2008 Brazilian study states that about 20% of Brazilian coffee production contains defective beans.6 In India, the beans rejected after sorting by size and colour, called triage, are about 15–20% of production.12 Defective beans add off-flavours and lower overall cup quality.11\n\nGrading systems weight defects differently. The Specialty Coffee Association (SCA) splits them into category 1 (primary) and category 2 (secondary) defects.18,15 One full black bean counts as much as three partial blacks.18,15 How defects are counted, and which grade a count gives, is explained in green coffee grading standards. This entry is about where each defect comes from.\n\n## Five places defects come from\n\nA defect is the visible end of a problem earlier in the chain. The sources place the causes at five stages:\n\n- **Field.** Insects, drought, poor nutrition and seed formation.8,5\n- **Harvest and wet mill.** Unripe or fallen fruit, delays, over-fermentation and badly set pulpers.2,3\n- **Drying.** Rewetting, too much heat and dirty drying yards.2,3,5\n- **Dry mill.** Hullers that are badly set, and coffee that is too dry or too wet.3,5\n- **Storage and transport.** Moisture taken up from the air, and pests.2,1\n\nProcessing weighs heavily. A 2016 Cenicafé paper estimates that more than 80% of bean defects come from poor processing and drying. They include vinegar, discoloured, soft (*flojo*) and mouldy beans.9 Soft beans are put down to a lack of drying.16\n\n
\n
\n
Where green coffee defects arise, from field to warehouse, with the sources that name each cause. Schematic; several defects have more than one cause.1,2,3,4,5,6,7,8,16
\n
\n\n## Defects that start in the field\n\n**Insect damage.** Insects bore into the fruit while it grows on the tree; the coffee berry borer is the main pest named.15,8 The seed is left with small, round holes.2 Bored beans ferment faster because of the physical damage.7 A Brazilian guide separates clean bored beans from bored beans with fungi in the holes.5\n\n**Immature beans.** They come from fruit picked before it is ripe.2,5 In the green bean, the silverskin sticks to the seed and the groove on its flat side is closed.4 They make the cup more astringent.6 Some immature beans stay pale when roasted; these are called quakers.10\n\n**Poorly filled and shell beans.** A poorly filled bean has little mass; a Brazilian guide links it to water or nutrient shortage and genetics.4,5 A shell forms when two interlocked seeds separate.4\n\n**Black and sour beans** can also start on the tree. Water shortage during fruit development (sour) and carbohydrate deficiency from poor farming practice (black) are among the causes named.6\n\n## Defects made in processing, drying and milling\n\n**Black beans.** Fruit that is overripe or lies on the ground ferments, and dries badly with spells of wetting.2,6 The result makes the cup bitter and disagreeable.2\n\n**Sour beans.** Brazil defines them as brown, in various shades, from the action of fermentation.4 They form when fresh cherry is left in sacks or heaps for many hours, or dried in too thick a layer.5\n\n**Stinkers.** They look normal or nearly so, but release a putrid odour when cut.2 Their taste carries into the beverage and makes it undrinkable.2 Over-long fermentation, unclean water and dirty tanks are the usual causes.2,3\n\n**Nipped and broken beans.** A pulper set too tight nips the beans.2,14 Beans break mostly in the huller, when the coffee is too dry.2 Broken beans roast faster than whole ones and tend to char.2\n\n**Drying faults.** Rewetting during drying lets mould grow.1,3 Too much heat gives reddish “foxy” beans and glassy beans.2\n\n**Milling leftovers.** Dried cherries (pods), parchment and husk stay in the coffee when the huller is badly set. Stones and sticks come from sweeping the drying yard.5\n\n## Defects that appear in storage\n\nDried coffee can take up water again. Above 80% relative humidity, stored coffee starts to absorb water.1 Mouldy beans give off a musty odour that does not disappear in roasting and passes into the cup.2 Warm, damp storage also fades the beans and gives aged, woody or earthy flavours.3,7 Weevils attack coffee in warehouses.1,16 Warehouse practice is covered in green coffee storage.\n\n\n\n## Reference table: defect, cause, cup\n\nThe table gives, for each physical defect, the stage where its cause lies, how it looks and what it can do to the cup, as stated in the sources. Weights for counting are in green coffee grading standards. “Not established” means no source opened for this entry states it.\n\n| Defect | Cause class | Cause in the sources | Visual cue | Likely cup effect | Prevention |\n|---|---|---|---|---|---|\n| Full black | Field; harvest and wet mill; drying | Overripe cherries on the soil, microbial fermentation; carbohydrate deficiency from poor agricultural practice6; prolonged fermentation of ground cherries, poor drying with wetting2; green beans fermenting in the coffee mass7 | Opaque black bean or piece4; at least half-black outside or inside2 | Bitter, disagreeable, generally undrinkable2; acrid and carbonous7; highest ochratoxin A with sour1 | Do not collect fallen fruit, above all in humid conditions; avoid rewetting1 |\n| Partial black | As full black | Not separately established | Less extensive blackening; three partials count as one full black (SCA)18,15 | Not established | As full black |\n| Black-green (*preto-verde*) | Drying | Immature seed exposed to high temperature5; inadequate drying of immature beans6 | Black bean, shiny because the silverskin adheres4 | Serious defect that strongly affects the cup6 | Pick ripe fruit; control drying heat5 |\n| Full sour (*ardido*) | Field; harvest and wet mill; drying | Water shortage in fruit development or abnormal fermentation6; fermentation, possibly on the plant; cherry bagged or heaped for many hours; drying layer too thick5 | Brown bean or piece, various shades4 | Highest ochratoxin A with black1 | Process cherry within hours; avoid thick drying layers5,7 |\n| Partial sour | As full sour | Not separately established | Less extensive than full sour; not defined in the sources opened | Not established | As full sour |\n| Vinegar (*vinagre*, Colombian class) | Harvest and wet mill | Over-fermentation; bean tissue affected after 70 h7; dry fermentation of unsorted coffee8; poor washing9 | Stained parchment7 | Sour flavour, vinegar aroma7; fermented and stinker aroma and acidity, onion-like, foul, nauseating8 | Sort cherry; control fermentation time; wash well8,9 |\n| Stinker | Harvest and wet mill | Excessively long fermentation or unclean water; badly cleaned tanks or channels2; a few extremely over-fermented beans left by poor tank hygiene; nipped beans3; residue left in the pulper14 | None or slight; putrid, nauseating odour when cut2 | Foul, rotten or sour3; undrinkable2 | Clean tanks, channels and pulper; clean water2,14 |\n| Fungus damage, mouldy | Harvest and wet mill; drying; storage | Mucilage left by poor washing; storing partly dried or too-wet coffee3; moisture uncontrolled in drying and storage8; moisture re-absorbed in store or transport2 | Partly or wholly covered with mould2; dirty look, greyish, yellow or whitish8 | Mouldy, musty3; mould, earth and damp8; odour survives roasting2; ochratoxin A risk1,15 | Avoid rewetting; protect stored coffee from humidity1 |\n| Insect damage (field) | Field | Insects boring into fruit on the tree15; mainly the coffee berry borer8 | Small, round holes2; one or more holes4; with or without fungi in the holes5 | Bored beans ferment faster; at high borer damage, nauseating, contaminated, carbonous aroma and flavour7 | Borer control on the farm (see coffee berry borer) |\n| Insect damage (storage) | Storage | Weevils1,16 | Holes (not described separately) | Not established | Integrated pest management in the warehouse1 |\n| Immature, unripe (*verde*) | Field (harvest decision) | Fruit picked weeks before ripeness2; picked before ideal maturity5 | Silverskin adhering, ventral groove closed4 | Astringency6; astringent acidity, fermented7; green, grassy3 | Pick ripe; remove unripe fruit before processing1 |\n| Quaker | Field (immature seed) | Chemical composition of the immature bean10 | Visible only after roasting: pale beans10 | At Agtron 82.8 or lighter, lowered sensory quality from 7 quakers in a cup of 65 beans (natural coffees)10 | As immature |\n| Withered, poorly filled (*mal granado*, *chocho*) | Field | Water or nutrient deficit, genetic factors5 | Incomplete formation, little mass4 | Not established | Not established |\n| Shell (*concha*) | Field (seed formation) | Separation of interlocked beans4, which form for genetic, physiological or climatic reasons5 | Shell-shaped bean4 | Not established | Not established |\n| Floater | Field (cherry) | Overripe and undeveloped cherries13; insect-damaged, dried and low-density fruit14 | Cherry floats in water13; green-bean floaters not described in the sources opened | Not established | Separate floaters in water before pulping14,13 |\n| Pulper-nipped | Wet mill | Pulper badly adjusted2,3 or set too tight14 | Parchment nipped off, naked or white beans14 | Linked to stinkers3 | Adjust the pulper; check beans regularly14; monitor broken, nipped and naked beans1 |\n| Broken, chipped, cut (*quebrado*) | Wet mill; drying; dry mill | In a depulper or at the dry mill15; hulling coffee that is too dry2; over-drying3,13; badly set hullers5 | Piece of bean, variable shape or size4 | Roasts faster, tends to char2 | Avoid over-drying; set the huller3 |\n| Crushed | Dry mill | Coffee too wet in the huller3; processing insufficiently dried coffee2 | Rather flat bean, median furrow laid open2 | Not established | Dry fully before hulling3 |\n| Foxy | Drying | Over-done artificial drying: high temperature, long drying, too little mixing2 | Red colouring2 | Not established | Control dryer temperature; mix2 |\n| Glassy | Drying | Artificial drying too hot at the start2 | White, opalescent, glassy; less dense2 | Not established; undesirable2 | Start drying gently2 |\n| Faded, aged (*decolorado*, *reposado*) | Drying; storage | Uneven drying; drying above 55 °C; poor storage conditions8; storage above 12% moisture (basis not stated), 70% relative humidity and 20 °C7; hot, humid storage3 | Very light green, whitish8; faded colour3; whitish spots from poor drying or germination2 | Aged, old, phenolic, mouldy, earthy7; high, unpleasant bitterness8; woody3 | Dry evenly, not above 55 °C; store cool, below 20 °C8; store dry7 |\n| Dried cherry, pod (*coco*) | Dry mill | Husk not removed; huller badly regulated4,5 | Bean still in its dried husk4 | Husk can carry more ochratoxin A1 | Regulate the huller5 |\n| Parchment (*marinheiro*) | Dry mill | Parchment not, or only partly, removed4; huller badly regulated5 | Bean with parchment4 | Not established | Regulate the huller5 |\n| Hull, husk (*casca*) | Dry mill | Husk removed but not winnowed out5; huller badly regulated4 | Fragment of dried husk4 | Can carry more ochratoxin A1 | Regulate huller and aspiration5 |\n| Foreign matter (stones, sticks, clods) | Drying | Sweepings from the drying yard4,5 | Stone, clod or twig fragment4 | Drying on the ground: earthy3 | Clean drying surfaces; sorting3,1 |\n| Amber, “buttery” (*ámbar*, *mantequilla*) | Not established | Not established | Listed in Colombia’s first defect group9 | Not established | Not established |\n\nTwo cautions apply. First, “cause class” names where a cause is reported, not how often it occurs. Second, the national names do not map one to one. The Brazilian *ardido* and the Colombian *vinagre* are separate classes in their own systems, and the SCA terms “withered” and “poorly filled” are matched here only by their description.4,9\n\n
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Defect-to-cause map: a filled dot marks each stage at which at least one source names a cause of the defect. Qualitative; a dot does not show how often a stage causes it.1,2,3,4,5,6,7,8,9,10,13,14,15,16
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\n\n## Reading a defect for its cause\n\nSome defects carry a clue to the stage that caused them.\n\n- **Bored beans with or without fungi.** The Brazilian guide counts “clean” and “dirty” bored beans apart; dirty ones have fungi in the holes.5\n- **White, naked beans.** Parchment nipped off in the pulper points to a gap set too tight.14\n- **Black with shining silverskin.** A black-green bean is an immature seed damaged by heat.4,5\n- **Whitish spots.** They reveal poor drying, or the start of germination with enzymatic reactions.2\n- **Red beans.** Foxy colouring points to over-done artificial drying.2\n- **Faded, whitish beans.** Uneven or too-hot drying, or poor storage.8,7\n\nSeveral strong cup defects leave no mark. The SCA notes that phenolic, potato and mould defects are usually not visible to the naked eye.15 Stinkers too look normal or nearly so.2\n\n## Chemistry of defective beans\n\n**Volatile markers.** In a 2008 Brazilian study of raw defective beans, 2-methylpyrazine and 2-furylmethanol acetate were potential markers of immature beans, and butyrolactone of sour beans.6 Black beans from both lots were rich in aldehydes, but no single marker was confirmed.6\n\n**Metabolite profiles.** A 2017 study split arabica into defective and non-defective fractions. Seventeen compounds, including organic acids, amino acids and reducing sugars, separated green defective from sound beans; 35, dominated by volatile compounds, organic acids, sugars and sugar alcohols, separated them after roasting.11 Three roasted-bean markers – 1-methylpyrrole, 5-methyl-2-furfurylfuran and 2-methylfuran – occurred only in the defective fractions.11\n\n**Physical properties.** Indian triage beans were lower in weight, density and brightness than graded beans, and lower in caffeine.12\n\n**Quakers.** In natural specialty coffees, quakers at Agtron 82.8 or lighter lowered sensory quality from 7 quakers in a cup of 65 beans.10 Their colour and sensory character follow from the composition of the immature bean.10 The roasting side is covered in roast defects.\n\n## Defects and food safety\n\nDefects matter for safety as well as flavour. The Codex code of practice states that defective beans and husk sometimes contain more ochratoxin A than sound beans.1 In lower-grade coffee, fruits with black and sour defects contained the highest levels.1 The code asks producers to remove defects before they enter the food chain, and says sorted-out beans should not be blended back into clean coffee or sold directly to roasters unless sampling and ochratoxin A analysis show them to be acceptable.1\n\nThe same code ties the main risks to the stages above. Fallen berries should not be collected, above all in humid conditions.1 Five days or less in the drying yard was enough to prevent ochratoxin A accumulation in the experiments it cites.1 Physical damage makes coffee more susceptible to contamination.1 An SCA research programme leaves fungus-damaged beans out of its sensory tests because of the health risk, and analyses them chemically, including for ochratoxin.15 The toxin itself is covered in ochratoxin A.\n\n## Defects by process and grade\n\nA 2009 Korean study of green coffees graded NY2 to NY4/5 found that the share of defective beans rose as sensory scores fell.17 No black or sour beans were found in the NY2 grade.17 In a Colombian survey of 162 farm samples, coffee grown below 1,300 m had more bored, vinegar and discoloured beans; bored beans averaged 3.78% of the sample there.9 Nipped beans were more frequent in farm-processed samples and in samples dried in mechanical dryers.9\n\n## Open questions\n\n- **Sensory weight of each defect.** An SCA-led programme is setting perception thresholds for category 1 and 2 defects by spiking clean coffee; no results were published in the sources opened.15\n- **Partial blacks and sours.** No source opened gives a separate cause for partial and full forms.\n- **Withered, shell and floater beans in the cup.** No source opened measured their cup effect.\n- **Amber beans.** Listed as a defect in Colombia9. A Colombian extension leaflet appears to link them to soil nutrient problems, but its layout leaves the link unclear16; no other source opened gives a cause.\n- **Wet-mill versus dry-mill cuts.** Whether a cut made in the pulper can be told from one made in the huller by the colour of the cut is not described in the sources opened.\n- **How often each stage causes each defect.** The cause map is qualitative; only one survey gave an estimate, for processing and drying faults.9\n\n## Key studies\n\n
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Toci & Farah, 2008 – Volatile markers of defective beans. Black, sour, immature and black-immature beans from two Brazilian lots were analysed raw and roasted. The authors propose candidate volatile markers for immature and sour beans and summarise what is known of each defect’s origin.

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Food Chemistry 108(3), 1133–1141 · doi:10.1016/j.foodchem.2007.11.064

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Puerta-Quintero, 2016 – Physical quality of Colombian coffee. Measured the physical quality of 162 traceable farm samples against altitude, soils and processing practice. It estimates that most bean defects, among them vinegar, discoloured, soft and mouldy beans, come from processing and drying, while borer damage and dried “guayaba” beans begin in the field.

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Revista Cenicafé 67(1), 7–40 · full text

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Rabelo et al., 2021 – Quakers in natural coffees. Quakers of three colours were added in increasing numbers to natural specialty coffees and cupped. Pale quakers lowered the cup only from 7 per 65 beans, and their aroma traced back to the chemistry of the immature seed.

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Food Chemistry 342, 128304 · doi:10.1016/j.foodchem.2020.128304

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Casas et al., 2017 – Biochemical features of defective arabica. Profiled defective and non-defective fractions before and after roasting. Green defective beans differed in acids, amino acids and sugars; three volatile markers appeared only in roasted defective fractions.

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Food Research International 95, 59–67 · doi:10.1016/j.foodres.2017.02.015

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