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Post-harvest processing · Method

Natural process

A processing method in which the whole coffee cherry is dried with its skin and pulp on, and the dried fruit is removed afterwards.

Source-checkedby Coffearium verification pass· Last source-checked 8 Oct 2026· Prepared with AI assistance· 14 sources (13 tier A)· 4 contested· Updated 8 Oct 2026
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Contents
  • 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
Pulping Mucilage Drying Hulling
Natural None Left on Whole cherry Husk off
Washed Skin + pulp off Fermented, washed Parchment Parchment off
Semi-dryincl. honey Skin + pulp off Left on Parchment + mucilage Parchment off

step takes place step skipped · all three end as green coffee

What stays on the seed during drying in the three processing families.

How it is done#

  1. Drying the whole cherry – the harvested cherries are dried in the sun1 – on patios or raised beds5 – or in drying machines.1
  2. 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
  3. 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
  4. 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
  5. Hulling – the dried husk (skin, pulp, mucilage and parchment) is removed mechanically, together with as much silverskin as possible.2

Effect on the cup#

Whether 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

Reference protocol#

The table brings together the parameters reported in the sources. It describes the range found in practice and research, not a single correct recipe.

Step Parameter Value reported Source
Drying surface Patio Thin layers of 2–5 cm on cement, brick or asphalt Duque-Dussán et al.5
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
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
Layer Depth and turning 2–3 cm, turned at least 10 times a day in both directions São Paulo manual11
Protection Heaping and covering Ventilate at night at first; heap and cover after about three days Codex1
Protection Heaping and covering Cover every night and in rain FAO Lao PDR manual12
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
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
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
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
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
Hulling Output About 1 kg of husk per kg of coffee bean produced Eckhardt et al.10
05101520253035daysFAO manual, Lao PDR18–20 days12 2026 reviewover three weeks5 2023 review, in the sun20–30 days13
Data table
daysSource
FAO manual, Lao PDR18–20 days12
2026 reviewover three weeks5
2023 review, in the sun20–30 days13
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

What happens inside the drying cherry#

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

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

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

Drying risks#

  • 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
  • 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
  • Mixed lots – the Codex code advises against mixing different types of coffee or coffee from different harvest days.1
  • 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
  • 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

Mixed evidence on flavour#

The 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.

Key studies#

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.

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

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.

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

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.

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

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.

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

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

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

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.
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Sources

  1. ACodex Alimentarius Commission (FAO/WHO) (2009). Code of Practice for the Prevention and Reduction of Ochratoxin A Contamination in Coffee (CAC/RCP 69-2009). Codex Alimentarius.
  2. ABobková, A.; Poláková, K.; Demianová, A.; Belej, Ľ.; Bobko, M.; Jurčaga, L.; Gálik, B.; Novotná, I.; Iriondo-DeHond, A.; del Castillo, M. D. (2022). Comparative Analysis of Selected Chemical Parameters of Coffea arabica, from Cascara to Silverskin. Foods 11(8), 1082. doi:10.3390/foods11081082 · other copies
  3. BHaile, M.; Kang, W. H. (2019). The Harvest and Post-Harvest Management Practices' Impact on Coffee Quality. Coffee – Production and Research, IntechOpen. doi:10.5772/intechopen.89224 · other copies
  4. ATeran, E. (2024). Enhancement of Coffee Quality Attributes by Combining Processing Methods and Varieties. Beverages 10(1), 10. doi:10.3390/beverages10010010 · other copies
  5. ADuque-Dussán, E.; Figueroa-Varela, P. A.; Cruz-Ospina, V.; Banout, J. (2026). Advances in coffee drying: A comprehensive review of traditional, solar, mechanical, hybrid, and emerging methods. Foods 15(10), 1737. doi:10.3390/foods15101737 · other copies
  6. ABorém, F. M.; Isquierdo, E. P.; Alves, G. E.; Ribeiro, D. E.; Siqueira, V. C.; Taveira, J. H. S. (2018). Quality of natural coffee dried under different temperatures and drying rates. Coffee Science 13(2). doi:10.25186/cs.v13i2.1410 · other copies
  7. ADe Bruyn, F.; Zhang, S. J.; Pothakos, V.; Torres, J.; Lambot, C.; Moroni, A. V.; Callanan, M.; Sybesma, W.; Weckx, S.; De Vuyst, L. (2017). Exploring the impacts of postharvest processing on the microbiota and metabolite profiles during green coffee bean production. Applied and Environmental Microbiology 83(1), e02398-16. doi:10.1128/AEM.02398-16 · other copies
  8. ABytof, G.; Knopp, S.-E.; Kramer, D.; Breitenstein, B.; Bergervoet, J. H. W.; Groot, S. P. C.; Selmar, D. (2007). Transient occurrence of seed germination processes during coffee post-harvest treatment. Annals of Botany 100(1), 61–66. doi:10.1093/aob/mcm068 · other copies
  9. AKleinwächter, M.; Selmar, D. (2010). Influence of drying on the content of sugars in wet processed green Arabica coffees. Food Chemistry 119(2), 500–504. doi:10.1016/j.foodchem.2009.06.048 · other copies
  10. AEckhardt, S.; Franke, H.; Schwarz, S.; Lachenmeier, D. W. (2022). Risk Assessment of Coffee Cherry (Cascara) Fruit Products for Flour Replacement and Other Alternative Food Uses. Molecules 27(23), 8435. doi:10.3390/molecules27238435 · other copies
  11. ASistema de Qualidade de Produtos Agrícolas, Pecuários e Agroindustriais do Estado de São Paulo Manual de Qualidade: Boas Práticas de Produção de Café. Secretaria de Agricultura e Abastecimento do Estado de São Paulo (Codeagro).
  12. AWinston, E.; Op de Laak, J.; Marsh, T.; Lempke, H.; Chapman, K. (2005). Arabica coffee manual for Lao-PDR. FAO Regional Office for Asia and the Pacific, Bangkok.
  13. AElhalis, H.; Cox, J.; Zhao, J. (2023). Coffee fermentation: Expedition from traditional to controlled process and perspectives for industrialization. Applied Food Research 3(1), 100253. doi:10.1016/j.afres.2022.100253 · other copies
  14. AAlves, G. E.; Borém, F. M.; Isquierdo, E. P.; Siqueira, V. C.; Cirillo, M. A.; Pinto, A. C. F. (2017). Physiological and sensorial quality of Arabica coffee subjected to different temperatures and drying airflows. Acta Scientiarum. Agronomy 39(2), 225–233. doi:10.4025/actasciagron.v39i2.31065 · other copies

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

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