{ "id": "natural-process", "url": "https://coffearium.org/entries/natural-process/", "license": "CC-BY-4.0", "title": "Natural process", "summary": "A processing method in which the whole coffee cherry is dried with its skin and pulp on, and the dried fruit is removed afterwards.", "domain": "post-harvest-processing", "kind": "Method", "stage": "process", "topics": [], "topicSections": {}, "lang": "en", "status": "verified", "reviewer": "Coffearium verification pass", "lastVerified": "2026-10-08T00:00:00.000Z", "updated": "2026-10-08T00:00:00.000Z", "brief": [ "The whole cherry is dried – in the sun or in drying machines – with its skin and pulp still on.1", "Drying the whole cherries takes about three to four weeks – 18–20 days in an FAO manual, 20–30 days in a 2023 review, over three weeks under favourable conditions in a 2026 review.12,13,5", "The dried husk is then removed mechanically, together with as much silverskin as possible.2" ], "quickFacts": [ { "label": "Fruit removed", "value": "After drying" }, { "label": "Drying time", "value": "18–20 days to 20–30 days, depending on source and climate (contested)" }, { "label": "Layer depth", "value": "3–5 cm, turned constantly" }, { "label": "Coffee (mass) temperature in dryers", "value": "≤ 45 °C (São Paulo state manual)" }, { "label": "Main microbes", "value": "Acetic acid bacteria and yeasts" }, { "label": "Dried as", "value": "Husk coffee (dried cherry)" }, { "label": "Protected from fungi", "value": "< 12.5% moisture (wet basis), water activity 0.67–0.70 (Codex, given for parchment coffee)" } ], "aka": [ "Dry process", "Unwashed" ], "linkTerms": [ "dry processing", "natural coffee", "natural coffees", "dry-processed", "naturals" ], "related": [ "coffee-cherry-anatomy", "washed-process", "drying", "microorganisms", "moisture-and-water-activity", "fermentation", "cherry-to-green-conversion" ], "contested": [ "Drying time for whole cherries: 18–20 days in an FAO manual for Lao PDR12; \"over three weeks under favourable conditions\" in a 2026 review5; 20–30 days in the sun in a 2023 review.13 The Codex code gives no total, but notes that 5 days or less in the drying yard while water activity is in the range where ochratoxin A fungi grow (0.80–0.95) is enough to prevent toxin accumulation.1", "Layer depth and night covering: the Codex code recommends 3–5 cm (thicker in dry regions), ventilation at night, and heaping and covering only after three days for cherry1; a São Paulo state manual uses 2–3 cm for naturals and heaps and covers from the half-dry stage11; an FAO manual for Lao PDR covers the coffee every night.12", "Drying temperature in mechanical dryers: a study on natural coffee recommends an air temperature of 35 °C for specialty coffee and advises against 45 °C6, while a 2026 review states that controlled drying at 40–50 °C best preserves quality, with 50 °C generally considered the maximum (it does not say whether this is air or coffee temperature).5", "Coffee (mass) temperature limit: a São Paulo state manual allows up to 45 °C in the coffee mass for natural coffee11, while Alves et al. (2017) state, citing earlier work, that coffee-mass temperatures above 40 °C cause thermal damage.14 These are limits on the coffee, not on the drying air." ], "corrections": [], "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": "Dry process: treatment of coffee cherries consisting in drying them, either under sunlight or in drying machines, to give husk coffee.", "accessed": "2026-09-30T00:00:00.000Z" }, { "id": "s2", "title": "Comparative Analysis of Selected Chemical Parameters of Coffea arabica, from Cascara to Silverskin", "authors": "Bobková, A.; Poláková, K.; Demianová, A.; Belej, Ľ.; Bobko, M.; Jurčaga, L.; Gálik, B.; Novotná, I.; Iriondo-DeHond, A.; del Castillo, M. D.", "year": 2022, "publisher": "Foods 11(8), 1082", "url": "https://www.mdpi.com/2304-8158/11/8/1082", "doi": "10.3390/foods11081082", "tier": "A", "quote": "The dried husk, consisting of skin, pulp, mucilage, and parchment, is removed, together with as much Silverskin as possible.", "accessed": "2026-09-30T00:00:00.000Z" }, { "id": "s3", "title": "The Harvest and Post-Harvest Management Practices' Impact on Coffee Quality", "authors": "Haile, M.; Kang, W. H.", "year": 2019, "publisher": "Coffee – Production and Research, IntechOpen", "url": "https://www.intechopen.com/chapters/70151", "doi": "10.5772/intechopen.89224", "tier": "B", "quote": "The type of coffee processing methods (wet and dry) that are performed to obtain the green beans determined the flavour properties and created a typical quality difference.", "accessed": "2026-09-30T00:00:00.000Z" }, { "id": "s4", "title": "Enhancement of Coffee Quality Attributes by Combining Processing Methods and Varieties", "authors": "Teran, E.", "year": 2024, "publisher": "Beverages 10(1), 10", "url": "https://www.mdpi.com/2306-5710/10/1/10", "doi": "10.3390/beverages10010010", "tier": "A", "quote": "specific Arabica varieties, such as Bourbon and Pacamara, enhance flavor when processed using the 'Natural/Dry' method", "accessed": "2026-09-30T00:00:00.000Z" }, { "id": "s5", "title": "Advances in coffee drying: A comprehensive review of traditional, solar, mechanical, hybrid, and emerging methods", "authors": "Duque-Dussán, E.; Figueroa-Varela, P. A.; Cruz-Ospina, V.; Banout, J.", "year": 2026, "publisher": "Foods 15(10), 1737", "url": "https://www.mdpi.com/2304-8158/15/10/1737", "doi": "10.3390/foods15101737", "tier": "A", "quote": "The maximum allowable drying temperature for coffee is generally considered to be 50 °C, as higher values increase the risk of chemical degradation and sensory deterioration", "accessed": "2026-09-30T00:00:00.000Z" }, { "id": "s6", "title": "Quality of natural coffee dried under different temperatures and drying rates", "authors": "Borém, F. M.; Isquierdo, E. P.; Alves, G. E.; Ribeiro, D. E.; Siqueira, V. C.; Taveira, J. H. S.", "year": 2018, "publisher": "Coffee Science 13(2)", "url": "https://coffeescience.ufla.br/index.php/Coffeescience/article/view/1410", "doi": "10.25186/cs.v13i2.1410", "tier": "A", "quote": "the temperature of 35º C is recommended for the production of specialty coffees the temperature of 45º C is not.", "accessed": "2026-09-30T00:00:00.000Z" }, { "id": "s7", "title": "Exploring the impacts of postharvest processing on the microbiota and metabolite profiles during green coffee bean production", "authors": "De Bruyn, F.; Zhang, S. J.; Pothakos, V.; Torres, J.; Lambot, C.; Moroni, A. V.; Callanan, M.; Sybesma, W.; Weckx, S.; De Vuyst, L.", "year": 2017, "publisher": "Applied and Environmental Microbiology 83(1), e02398-16", "url": "https://journals.asm.org/doi/10.1128/aem.02398-16", "doi": "10.1128/AEM.02398-16", "tier": "A", "quote": "During dry processing, acetic acid bacteria (i.e., Acetobacter and Gluconobacter) were most abundant, along with Pichia and non-Pichia (Candida, Starmerella, and Saccharomycopsis) yeasts. Accumulation of associated metabolites (e.g., gluconic acid and sugar alcohols) took place in the drying outer layers of the coffee cherries.", "accessed": "2026-09-30T00:00:00.000Z" }, { "id": "s8", "title": "Transient occurrence of seed germination processes during coffee post-harvest treatment", "authors": "Bytof, G.; Knopp, S.-E.; Kramer, D.; Breitenstein, B.; Bergervoet, J. H. W.; Groot, S. P. C.; Selmar, D.", "year": 2007, "publisher": "Annals of Botany 100(1), 61–66", "url": "https://academic.oup.com/aob/article/100/1/61/2763338", "doi": "10.1093/aob/mcm068", "tier": "A", "quote": "The highest germination activity occurred 2 d after the onset of wet processing, whereas the corresponding maximum in the course of dry processing appeared about 1 week after the start of post harvest treatment.", "accessed": "2026-09-30T00:00:00.000Z" }, { "id": "s9", "title": "Influence of drying on the content of sugars in wet processed green Arabica coffees", "authors": "Kleinwächter, M.; Selmar, D.", "year": 2010, "publisher": "Food Chemistry 119(2), 500–504", "url": "https://doi.org/10.1016/j.foodchem.2009.06.048", "doi": "10.1016/j.foodchem.2009.06.048", "tier": "A", "quote": "the lower contents of glucose and fructose generally present in wet processed coffee beans in comparison to dry processed ones are - at least in part - due to metabolic processes", "accessed": "2026-09-30T00:00:00.000Z" }, { "id": "s10", "title": "Risk Assessment of Coffee Cherry (Cascara) Fruit Products for Flour Replacement and Other Alternative Food Uses", "authors": "Eckhardt, S.; Franke, H.; Schwarz, S.; Lachenmeier, D. W.", "year": 2022, "publisher": "Molecules 27(23), 8435", "url": "https://www.mdpi.com/1420-3049/27/23/8435", "doi": "10.3390/molecules27238435", "tier": "A", "quote": "Dry processing produces about 1 kg of coffee husk for every kg of coffee bean produced.", "accessed": "2026-09-30T00:00:00.000Z" }, { "id": "s11", "title": "Manual de Qualidade: Boas Práticas de Produção de Café", "authors": "Sistema de Qualidade de Produtos Agrícolas, Pecuários e Agroindustriais do Estado de São Paulo", "publisher": "Secretaria de Agricultura e Abastecimento do Estado de São Paulo (Codeagro)", "url": "https://codeagro.agricultura.sp.gov.br/arquivos/selo/3_superior92a8c870bc4c066dbd645dc06fbdd7b0.pdf", "tier": "A", "quote": "Não deixe a temperatura da massa de café ultrapassar 45ºC", "accessed": "2026-09-30T00:00:00.000Z" }, { "id": "s12", "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": "Drying cherry coffee may take 18 to 20 days. Parchment coffee dries in about 9 to 10 days.", "accessed": "2026-09-30T00:00:00.000Z" }, { "id": "s13", "title": "Coffee fermentation: Expedition from traditional to controlled process and perspectives for industrialization", "authors": "Elhalis, H.; Cox, J.; Zhao, J.", "year": 2023, "publisher": "Applied Food Research 3(1), 100253", "url": "https://www.sciencedirect.com/science/article/pii/S2772502222002086", "doi": "10.1016/j.afres.2022.100253", "tier": "A", "quote": "The sinkers (mature cherries) are spread on the ground or platforms under the sun for 20-30 days until the moisture content from 60-65 % (wb) reaches about 12 %", "accessed": "2026-10-08T00:00:00.000Z" }, { "id": "s14", "title": "Physiological and sensorial quality of Arabica coffee subjected to different temperatures and drying airflows", "authors": "Alves, G. E.; Borém, F. M.; Isquierdo, E. P.; Siqueira, V. C.; Cirillo, M. A.; Pinto, A. C. F.", "year": 2017, "publisher": "Acta Scientiarum. Agronomy 39(2), 225–233", "url": "https://www.redalyc.org/journal/3030/303050431012/html/", "doi": "10.4025/actasciagron.v39i2.31065", "tier": "A", "quote": "coffee that is processed via a dry method is more sensitive to mechanical drying with heated air than coffee processed via a wet method, resulting in poor physiological performance", "accessed": "2026-09-30T00:00:00.000Z" } ], "markdown": "
\n
\n
What stays on the seed during drying in the three processing families.
\n
\n\n## How it is done\n\n1. **Drying the whole cherry** – the harvested cherries are dried in the sun1 – on patios or raised beds5 – or in drying machines.1\n2. **Thin layers, turned often** – the Codex code of practice recommends layers of only 3–5 cm, turned constantly during the day. This speeds up drying and reduces the risk of mould.1\n3. **Protection** – at first, wet cherries need ventilation at night to avoid condensation. After about three days they can be heaped and covered at night or in rain so that they do not get wet again.1 Practice varies: some guides cover every night (see Deep dive).12\n4. **Drying to a safe level** – drying takes about three to four weeks: 18–20 days in one FAO manual, over three weeks under favourable conditions in a 2026 review,12,5 and 20–30 days in the sun in a 2023 review, which gives the moisture falling from 60–65% (wet basis) to about 12%.13 A São Paulo state manual sets the end point at 11% moisture (basis not stated).11 The Codex code considers parchment coffee protected from fungal damage below 12.5% moisture (wet basis) and a water activity of at most 0.67–0.70.1\n5. **Hulling** – the dried husk (skin, pulp, mucilage and parchment) is removed mechanically, together with as much silverskin as possible.2\n\n## Effect on the cup\n\nWhether coffee is processed wet or dry creates typical differences in quality and flavour.3 A 2024 study found that some Arabica varieties, such as Bourbon and Pacamara, scored better for flavour when processed natural.4\n\n\n\n## Reference protocol\n\nThe table brings together the parameters reported in the sources. It describes the range found in practice and research, not a single correct recipe.\n\n| Step | Parameter | Value reported | Source |\n|---|---|---|---|\n| Drying surface | Patio | Thin layers of 2–5 cm on cement, brick or asphalt | Duque-Dussán et al.5 |\n| Drying surface | Raised beds | Air flows under the coffee; more uniform drying and fewer anaerobic conditions; patios dry more slowly | Duque-Dussán et al.5 |\n| Layer | Depth and turning | 3–5 cm (25–35 kg of fresh cherry per m²), thicker in dry regions, turned constantly during the day | Codex1 |\n| Layer | Depth and turning | 2–3 cm, turned at least 10 times a day in both directions | São Paulo manual11 |\n| Protection | Heaping and covering | Ventilate at night at first; heap and cover after about three days | Codex1 |\n| Protection | Heaping and covering | Cover every night and in rain | FAO Lao PDR manual12 |\n| Duration | Drying whole cherries | 18–20 days; over three weeks under favourable conditions; 20–30 days in the sun | FAO Lao PDR manual12, Duque-Dussán et al.5, Elhalis et al.13 |\n| Duration | Critical window | 5 days or less in the drying yard at water activity 0.80–0.95 is enough to prevent ochratoxin A accumulation | Codex1 |\n| Mechanical drying | Drying temperature | Air at 35 °C recommended for specialty naturals (45 °C not); 40–50 °C best preserves quality, 50 °C generally the maximum, in a general review (air or coffee temperature not specified) | Borém et al.6, Duque-Dussán et al.5 |\n| Mechanical drying | Coffee (mass) temperature | ≤ 45 °C; ≤ 30 °C when many green fruits are present (São Paulo manual); above 40 °C causes thermal damage (Alves et al., citing earlier work) | São Paulo manual11, Alves et al.14 |\n| End point | Moisture | About 12%, from 60–65% (wb) at the start; 11% (basis not stated); protected from fungi below 12.5% (wb) with water activity at most 0.67–0.70 (given for parchment coffee) | Elhalis et al.13, São Paulo manual11, Codex1 |\n| Hulling | Output | About 1 kg of husk per kg of coffee bean produced | Eckhardt et al.10 |\n\n
\n
\n
Drying time for whole cherries in three sources. All point to around three weeks or more but do not agree on the figure.5,12,13
\n
\n\n\n## What happens inside the drying cherry\n\n**Microbes.** Natural processing hosts a different microbial community from washed processing. In a study in Ecuador, acetic acid bacteria (*Acetobacter* and *Gluconobacter*) were the most abundant, together with *Pichia* and other yeasts (*Candida*, *Starmerella*, *Saccharomycopsis*). Their products – gluconic acid and sugar alcohols – built up in the drying outer layers of the cherry.7\n\n**The seed.** The seed stays alive during drying and starts germination processes, just as in washed coffee – but later: in dry processing, germination activity peaked about one week after processing began, compared with about two days in wet processing.8\n\n**Sugars.** Natural coffees generally contain more glucose and fructose than washed coffees. A study of washed coffee during drying showed that this difference is due – at least in part – to metabolic processes, not to sugars leaching into the process water.9\n\n## Drying risks\n\n- **Mould and ochratoxin A** – whole cherries take weeks to dry. Thin layers and frequent turning are among the measures the Codex code gives against fungal growth.1\n- **Rewetting** – coffee can lose water quickly at midday and reabsorb moisture at night, and condensation can form inside passive dryers that are poorly ventilated.5 Rewetting favours fungal growth and ochratoxin A.1\n- **Mixed lots** – the Codex code advises against mixing different types of coffee or coffee from different harvest days.1\n- **Uneven or too-fast drying** – rapid, uneven moisture removal in mechanical dryers can cause casehardening, a hard outer shell that traps moisture inside; uneven or rapid drying can also degrade delicate aromatics and diminish fruity or floral notes.5\n- **Too-high temperature** – the quality of natural coffee depends on preserving the cell membranes of the seed, which can be damaged during drying.6 A São Paulo state manual separately limits the temperature of the coffee mass in dryers to 45 °C, and to below 30 °C when many green fruits are present.11 Alves et al. (2017) state, citing earlier work, that coffee-mass temperatures above 40 °C cause thermal damage that lowers quality (see Contested).14\n\n## Mixed evidence on flavour\n\nThe 2024 study that found benefits for Bourbon and Pacamara also found, across all Arabica samples, a tendency towards lower flavour scores for natural processing – a result that was not statistically significant.4 The effect of the natural process on the cup depends on the coffee it is applied to.\n\n## Key studies\n\n
\n

Borém et al., 2018 – Drying temperature and natural coffee quality. Dries natural coffee at 35, 40 and 45 °C and at two dew-point temperatures, and follows sensory, chemical and physiological quality. Recommends 35 °C for specialty coffee and advises against 45 °C.

\n

Coffee Science 13(2) · doi:10.25186/cs.v13i2.1410

\n
\n\n
\n

De Bruyn et al., 2017 – Microbiota and metabolites in wet and dry processing. Follows Typica coffee in Ecuador through standard and heaped dry processing and two wet variants, using DNA sequencing and metabolite analysis.

\n

Applied and Environmental Microbiology 83(1), e02398-16 · doi:10.1128/AEM.02398-16

\n
\n\n
\n

Duque-Dussán et al., 2026 – Advances in coffee drying. A review of sun, raised-bed, solar, mechanical, hybrid and emerging drying methods, their drying kinetics and their effect on quality.

\n

Foods 15(10), 1737 · doi:10.3390/foods15101737

\n
\n\n
\n

Bytof et al., 2007 – Germination during processing. Shows that germination processes in the seed peak about a week into dry processing, much later than in wet processing.

\n

Annals of Botany 100(1), 61–66 · doi:10.1093/aob/mcm068

\n
\n\n
\n

Teran, 2024 – Processing and variety. Analyses how processing method and variety interact in their effect on quality attributes of Arabica coffee.

\n

Beverages 10(1), 10 · doi:10.3390/beverages10010010

\n
" }