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Post-harvest processing · Method

Washed process

A processing method in which the skin, pulp and mucilage are removed from the coffee seed before it is dried.

Across the chain: Sustainability

Source-checkedby Coffearium verification pass· Last source-checked 8 Oct 2026· Prepared with AI assistance· 16 sources (14 tier A)· 3 contested· Updated 8 Oct 2026
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Contents
  • The skin and pulp are removed mechanically, in the presence of water.1
  • The remaining mucilage is broken down – usually by fermentation, sometimes with enzymes or machines – and washed off, leaving parchment coffee.1,3,5
  • The parchment coffee is dried until it is safe from fungal damage – below 12.5% moisture (wet basis) according to the Codex code of practice.1
Pulping Mucilage Drying Hulling
Washed Skin + pulp off Fermented, washed Parchment Parchment off
Semi-dryincl. honey Skin + pulp off Left on Parchment + mucilage Parchment off
Natural None Left on Whole cherry Husk 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. Selection – the process needs ripe cherries only, either picked selectively or separated mechanically during processing,1 for example in flotation tanks.11
  2. Pulping – a pulping machine removes the skin and pulp in the presence of water.1 The seeds are left covered in slimy mucilage, which pulping does not remove.1 In Kenya, the pulped coffee is then graded by density and size into grades 1 and 2 and “lights”.13
  3. Mucilage removal – the coffee is usually fermented in water at ambient temperature, so that microorganisms break the mucilage down.1 Some producers use enzymes instead.3
  4. Washing – the loosened mucilage is washed off. The result is called parchment or washed coffee.3 Some mills add a soak in clean water before the final wash (see below).13,14
  5. Drying – the parchment coffee is dried in thin layers of 3–5 cm and turned regularly.1 It is considered safe from fungal damage below 12.5% moisture (wet basis) and a water activity of 0.67–0.70.1

Soaking and grading#

Soaking. In some processing chains the washed parchment is held under clean water once more, from overnight up to, rarely, 48 hours.14 This is sometimes called secondary fermentation.14 In Kenya, about 12 hours of soaking after fermentation was found to improve colour and taste; the parchment is then washed again.13 Soaking is used to improve the look of the green bean and give a cleaner cup.5 In a trial in Yunnan, a 24-hour soak evened out the green coffee: it tempered the gains of longer fermentation, whatever had been done before.5 Short soaks do not seem to cause defects unless the water is tainted.14

Grading by density. Density sorting starts before pulping, when floating cherries are separated in water.1,11 In Kenya, the pulped coffee is graded again by density and size into grades 1 and 2 and “lights”.13 The final wash there is done in concrete channels, where the parchment is pushed with wooden paddles against a stream of water.13 In the Yunnan trial, washing was done by passing the beans through a curved water channel.5

Effect on the cup#

Whether coffee is processed wet or dry creates typical differences in quality and flavour.3 The effect is not the same for every coffee: a 2024 analysis of Coffee Quality Institute cupping records found that the effect of processing on flavour scores depended on the variety.4 Within the washed process, fermentation time matters too: in a controlled trial, a longer fermentation gave a fruitier and more acidic cup.5

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
Sorting Ripeness Ripe cherries only; floaters separated in water Codex1, Eckhardt et al.11
Pulping Method Mechanical, with water Codex1
Fermentation Medium and temperature Under water, ambient temperature Codex1
Fermentation Duration 12–36 h (Codex); 12–48 h (2016 review); 6–72 h depending on climate (2023 review) Codex1, Poltronieri & Rossi14, Elhalis et al.2
Fermentation pH course Starts at about 6.0–6.5, falls to about 4.0 Zhang et al.5
Alternative Mechanical demucilaging Cup quality comparable to fermented coffee in one trial Zhang et al.5
Grading Pulped parchment Grades 1, 2 and lights, by density and size (Kenya) FAO13
Soaking Duration About 12 h (Kenya); overnight to rarely 48 h; 24 h in one trial FAO13, Poltronieri & Rossi14, Zhang et al.5
Washing Final wash Concrete channels, parchment pushed against a stream of water (Kenya) FAO13
Water Use per kg dry parchment About 40 L conventional; under 1 L with the DESLIM mechanical demucilager Cenicafé9
Drying Layer depth 3–5 cm, turned constantly during the day Codex1
Drying Protection Parchment can be heaped and covered after one day of drying Codex1
Drying Drying temperature 40–50 °C recommended; maximum generally considered to be 50 °C Duque-Dussán et al.10
End point Storage safety < 12.5% moisture (wb), water activity 0.67–0.70 Codex1
0122436486072Hours of fermentationCodex code of practice12–36 h1 2016 review12–48 h14 2023 review, by climate6–72 h2 Yunnan trial, main pH drop36 h5
Data table
Hours of fermentationSource
Codex code of practice12–36 h1
2016 review12–48 h14
2023 review, by climate6–72 h2
Yunnan trial, main pH drop36 h5
Fermentation time as reported by the sources of this entry: Codex code of practice1, Poltronieri & Rossi14, Elhalis et al.2, Zhang et al.5 The ranges do not agree (see Contested).

Fermentation: microbiology and chemistry#

Wet fermentation is dominated by lactic acid bacteria. In a study in Ecuador, Leuconostoc, Lactococcus and Lactobacillus were the most common group, together with enterobacteria and the yeasts Pichia and Starmerella.6 A 2022 review names Leuconostoc pseudomesenteroides, Lactobacillus vaccinostercus, Lactobacillus brevis and Lactobacillus plantarum among the lactic acid bacteria that increase during fermentation.11

Their activity acidifies the fermentation water: in a trial in Yunnan, China, pH fell from about 6.0–6.5 to about 4.0 in every variant, with the largest drop after 36 hours.5 Lactic acid, acetic acid and mannitol formed in the mucilage were later found inside the seed.6

The seed’s own metabolism#

Processing does not only act on the outside of the seed. The seed is alive, and processing switches on germination processes inside it. In washed coffee, germination activity peaked about two days after processing began – much earlier than in natural coffee.7

Why washed coffee has less sugar#

Washed green coffee holds significantly less glucose and fructose than natural coffee processed in parallel, in a study of Arabica var. Acaiá.12 Two explanations are offered.

Seed metabolism. In washed coffee the two sugars fall during processing, while in natural coffee they stay the same or even rise.12 When Arabica that had been mechanically demucilaged and dry-fermented without water was dried under controlled conditions – with no process water present – glucose and fructose fell significantly within the first day.8 The authors concluded that the difference is, at least in part, due to metabolic processes and not to sugars leaching into the process water.8 A field study in Ecuador agrees for the tank stage: fructose, glucose and sucrose in the endosperm fell significantly during fermentation, and the authors put this down to the lack of oxygen under water, which triggered germination and an anaerobic sugar-consumption response in the seed.6

Loss into the water. The same Ecuadorian study found that fructose and glucose fell further during a 24-hour soak, and proposed that osmotic pressure helped monosaccharides and fermentation products leave the beans.6 In Yunnan, fructose was among the most abundant compounds in the soaking water at the end of soaking, and glucose and fructose in the beans dropped after washing.5

The two mechanisms are not exclusive. The evidence points to metabolism during fermentation and drying, with leaching adding to the loss where a soak is used.6,8 No study in this entry has measured how much of the final difference each one explains.

Mass balance#

Processing removes most of the cherry’s weight. Published conversion factors are rounded rules of thumb.

Parameter Value reported Source
Fresh cherry to green coffee (washed) About 5:1 often stated; usually about 6:1 in Ethiopia Schuit et al.15
Fresh cherry to green coffee 5–6 kg cherry per kg green European Coffee Federation16
Mucilage About 13% of the cherry’s weight; about 22% of pulped coffee Cenicafé9
Parchment husk About 20% of the weight of dry parchment coffee (1.25:1 parchment to green) Schuit et al.15

The sources opened for this entry give no primary figure for the share of skin and pulp on a fresh-weight basis, so it is left out.

Water and wastewater#

Conventional washing can use about 40 litres of water per kilogram of dry parchment coffee.9 The ecological processing developed by Cenicafé in Colombia pulps without water and removes mucilage mechanically; with its DESLIM demucilager, water use fell to under 1 litre per kilogram.9

Key studies#

Zhang et al., 2019 – Processing parameters in wet processing. A controlled trial in Yunnan (Catimor) comparing depulped and mechanically demucilaged coffee, standard and extended fermentation, and soaking. Longer fermentation gave a fruitier, more acidic cup; mechanical demucilaging matched the fermented coffee; soaking dampened the fermentation effects.

Frontiers in Microbiology 10, 2621 · doi:10.3389/fmicb.2019.02621

De Bruyn et al., 2017 – Microbiota and metabolites in wet and dry processing. Follows Typica coffee in Ecuador from harvest to drying with DNA sequencing and metabolite analysis. Wet processing was dominated by lactic acid bacteria, and several of their metabolites reached the seed.

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

Bytof et al., 2007 – Germination during processing. Measures germination markers in seeds during wet and dry processing and shows that their timing and extent differ between the two methods.

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

Kleinwächter & Selmar, 2010 – Sugars during drying. Dries Arabica that was mechanically demucilaged and dry-fermented without water, under defined conditions, and shows that glucose and fructose fall within the first day, with no process water present. The authors read this as evidence that metabolic processes, not leaching, explain at least part of the sugar gap between wet- and dry-processed coffees.

Food Chemistry 119, 500–504 · doi:10.1016/j.foodchem.2009.06.048

Teran, 2024 – Processing and variety. Analyses Coffee Quality Institute cupping records to see how processing method and variety interact in their effect on sensory scores of Arabica coffee.

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

Contested
  • Typical fermentation time: the Codex code of practice gives 12 to 36 hours1, a 2016 review gives 12 to 48 hours14, and a 2023 review gives 6 to 72 hours, depending on the surrounding climate.2
  • Flavour impact of fermentation metabolites: lactic acid, acetic acid and mannitol formed in the mucilage have been found in the seed6, but a 2023 review describes the migration of microbial metabolites into the seed as "believed" and their link to flavour as a correlation.2
  • Why washed green coffee has less glucose and fructose: a drying study attributes the loss at least in part to metabolic processes, not to leaching – sugars fell while wet-processed (mechanically demucilaged) Arabica dried, with no process water present8 – and an earlier comparison found that the two sugars decrease during wet processing but stay unchanged or rise during dry processing12; a field study links the drop during fermentation to anaerobic sugar consumption by the seed, but adds that during soaking osmotic pressure helped monosaccharides leave the beans.6 A trial in Yunnan found fructose among the most abundant compounds in the soaking water.5
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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. 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
  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. AZhang, S. J.; De Bruyn, F.; Pothakos, V.; Contreras, G. F.; Cai, Z.; Moccand, C.; Weckx, S.; De Vuyst, L. (2019). Influence of various processing parameters on the microbial community dynamics, metabolomic profiles, and cup quality during wet coffee processing. Frontiers in Microbiology 10, 2621. doi:10.3389/fmicb.2019.02621 · other copies
  6. 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
  7. 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
  8. AKleinwächter, M.; Selmar, D. (2010). Influence of drying on the content of sugars in wet processed green Arabica coffees. Food Chemistry 119, 500–504. doi:10.1016/j.foodchem.2009.06.048 · other copies
  9. ARoa, G.; Oliveros, C. E.; Álvarez, J.; Sanz, J. R.; Ramírez, C. A.; Dávila, M. T.; Álvarez, J. R.; Zambrano, D. A.; Puerta, G. I.; Rodríguez, N. Ecological Processing of Coffee at the Farm Level: An Ecological and Profitable Case. Cenicafé (Colombian Coffee Research Centre).
  10. 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
  11. 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
  12. AKnopp, S.; Bytof, G.; Selmar, D. (2006). Influence of processing on the content of sugars in green Arabica coffee beans. European Food Research and Technology 223, 195–201. doi:10.1007/s00217-005-0172-1 · other copies
  13. AMutua, J. (2000). Post Harvest Handling and Processing of Coffee in African Countries, Annex 5: Coffee Post Harvest Handling and processing in Kenya. FAO.
  14. APoltronieri, P.; Rossi, F. (2016). Challenges in Specialty Coffee Processing and Quality Assurance. Challenges 7(2), 19. doi:10.3390/challe7020019 · other copies
  15. ASchuit, P.; Moat, J.; Gole, T. W.; Challa, Z. K.; Torz, J.; Macatonia, S.; Cruz, G.; Davis, A. P. (2021). The potential for income improvement and biodiversity conservation via specialty coffee in Ethiopia. PeerJ 9, e10621. doi:10.7717/peerj.10621 · other copies
  16. BEuropean Coffee Federation The Journey of the Coffee Bean. European Coffee Federation.

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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