CoffeariumBeta
  1. Plant
  2. Farm
  3. Process
  4. Trade
  5. Roast
  6. Brew
  7. Cup
Post-harvest processing · Method

Wet-hulled (giling basah)

An Indonesian process in which pulped, briefly fermented parchment is hulled while still wet, at roughly 35–50% moisture content, and the naked green bean is then dried.

Source-checkedby Coffearium verification pass· Last source-checked 8 Oct 2026· Prepared with AI assistance· 12 sources (5 tier A)· 4 contested· Updated 8 Oct 2026
Reading depth
Contents
  • Cherries are pulped, fermented and washed, and the wet parchment is sun-dried only briefly before it changes hands.1,2
  • The parchment is hulled while the bean is still wet – at 40–45% moisture in the Mandheling trial, 35–45% or 40–50% in the FAO project report – and the naked bean is then dried to about 12%.1,2
  • Humid harvest weather and the need for quick cash are the reasons given for the practice.9,10,11
  • The green coffee is dark, opal-green, and the cup is known for low acidity, heavy body and earthy notes.1,8
  • Holding wet parchment for days raised mould and musty flavours in an FAO trial, and the naked bean must be dried at once to limit mould; rewetting favours fungal growth and ochratoxin A.2,4

What it is#

Wet hulling – giling basah in Indonesian – is a way of processing Arabica in which the parchment is taken off while the bean is still wet, and the naked bean is dried afterwards.1,8 In the washed process and in dry hulling, the parchment coffee is dried first, to about 12%, and only then hulled.1,3 In the trade the process is also called “semi-washed”11, but the same term is used elsewhere for other processes: the FAO uses it for coffee whose mucilage is removed by a demucilager straight after pulping, without fermentation6, and the Codex code of practice for green coffee from pulped beans dried within their mucilaginous parchment.4 This entry uses “wet-hulled” only.

The method is used in parts of Indonesia, above all Sumatra.8 Mandheling coffee from the highlands around Lake Toba in North Sumatra is made this way by smallholder farmers.1 It is also used in the Gayo highlands of Aceh3 and in Sulawesi.7,9 One importer reports that some buyers now ask for wet-hulled coffee from places such as Bali and Flores, which did not traditionally use it.7

FarmerCollectorHuller / millDay −1Day 0Day 1 to 14After hullingsells wetparchmentdelivered wet1Pulp fresh cherry 2 2Ferment overnight,then wash 2,7,10 3Partial sun-drying½ day (trial) to 1–2 days 1,2 4Wet parchment held in sacks41.7–54.0% moisture, 1 day to weeks 1 mould vs storage time: sources disagree 1,2 5Wet hulling at about 35–50% moisture 1,2 modified huller: rubber strip, 25 hp,750 rpm, about 800 kg/h 2 out: naked, swollen, whitish-green bean 8 6Dry the naked bean at once to 12% 1,2 7Sort, export: dark, opal-green coffee 8,12 Fully washed, for comparison: parchment dried to 12% first, then hulled dry 1 Roles vary by region; some collectors also pulp and ferment 9 . Schematic, not to scale.
Who does what along the wet-hulled chain, with the moisture values reported in trials; the fully washed route is shown for comparison. Roles vary by region. Schematic, not to scale.1,2,7,8,9

How it is done#

  1. Pulping and fermentation – the farmer pulps the cherries and ferments the pulped coffee, then washes it the next day.2 Importers describe the fermentation as overnight, in bags, tubs or tanks.7,10 In some areas the pulped seeds are instead held with their mucilage in tanks or sacks until delivery.11
  2. Brief drying in parchment – the wet parchment is sun-dried only briefly: half a day in an FAO trial, 1–2 days in North Sumatran practice.1,2
  3. Sale and holding – the farmer sells the wet parchment to a collector.2,9 In North Sumatra it may be stored for up to a few weeks before hulling; in a 2004/05 trial2 the stored parchment held 41.74–53.96% moisture.1
  4. Wet hulling – a huller, usually owned by the mill, takes off the parchment while the bean is still wet: at 40–45% moisture in the Mandheling trial, 35–45% (huller) or 40–50% (practice) in the FAO report.1,2,9 The bean that comes out is swollen with water and white7 or whitish-green.8
  5. Drying the naked bean – the green bean is dried straight after hulling, to limit mould,2 down to about 12% moisture.1,2 It then goes through the usual sorting before export.9

Why it arose#

The sources give two reasons. The first is climate. Rain and humidity are high in the growing regions, which makes it hard to dry parchment coffee fully; taking the parchment off early reduces the mass and shortens drying.9,10,11 The second is money. Smallholders can sell wet parchment soon after harvest, so cash comes in quickly at every link of the chain.7,9,10 One importer adds market access and local tradition to the list.11

The structure of the trade follows from this. Farmers process small lots, collectors buy and gather the wet parchment, and the miller owns the wet huller.2,9 In some places collectors also do the pulping and fermentation.9

Appearance and cup#

Green coffee. Wet-hulled coffee is dark, opal-green, with little silverskin left on the bean.8 Because the bean is soft when it passes through the huller, many beans come out with crushed or split ends.7

Cup. Mandheling coffee is described as low in acidity, with a heavy, complex body and spicy, slightly earthy and fruity flavour.1 A trial in Gayo found the same pattern – low acidity and strong body – and tasters preferred wet-hulled over dry-hulled coffee.3 One importer lists earthy, savoury, herbaceous and dark-chocolate notes11; another treats herbal, mossy and mushroomy notes as signs of faults in processing, though it notes that a slight green-herb note can be pleasant.7 The authors of the North Sumatran trial suggest that the handling itself contributes to this character.1

Reference protocol#

The table brings together the parameters reported in the sources. It describes the range found in practice and in trials, not a single correct recipe. Moisture values are given as reported; the trial reports do not state the basis, and the FAO trial determined moisture by oven drying (105 °C, 24 h).2

Parameter Value reported Source
Pulping By the farmer, on the day of harvest (trial Day −1) FAO trial report2
Fermentation After pulping, then washed; described as overnight FAO2, importers7,10
Partial drying in parchment Half a day (trial); 1–2 days of sun (North Sumatra) FAO2, Ismayadi et al.1
Moisture of wet parchment in storage 41.74–53.96% Ismayadi et al.1
Storage before hulling Up to a few weeks in practice; 1, 7 and 14 days tested, in PE sacks in a warehouse Ismayadi et al.1
Moisture at hulling 40–45% (Mandheling trial); 35–45% (FAO, modified huller) and 40–50% (FAO, North Sumatran practice); the Gayo trial’s value lies within this range Ismayadi et al.1, FAO2, Abubakar et al.3
Huller Indonesian Kemajuan huller, steel huller bar replaced by a rubber strip FAO2
Huller power and speed Raised from 15 to 25 hp and from 600 to 750 rpm FAO2
Huller throughput About 800 kg of wet green bean per hour FAO2
After hulling Dry immediately FAO2
Intermediate holding (trial variant) Dried to 17%, held 3 weeks, then dried to 12% Ismayadi et al.1
Final moisture 12% Ismayadi et al.1, FAO2
Safe for parchment coffee Moisture < 12.5% (wet basis) and water activity at most 0.67–0.70 Codex4
Fully washed control Fresh parchment dried to 12% before hulling Ismayadi et al.1
0102030405060moisture content, % as reported (basis not stated; Codex: wet basis)Wet-hulled: wet parchmentas stored before hulling(trial, North Sumatra)41.7–54.01 Wet-hulled: at wet hulling(Ismayadi et al., Mandhelingtrial)40–451 Wet-hulled: at wethulling, modified huller(FAO report)35–452 Wet-hulled: at wethulling, North Sumatranpractice(FAO report)40–502 Wet-hulled: optionalintermediate holding(trial)17, held 3 weeks1 Wet-hulled: naked bean,final drying121,2 Fully washed control:parchment dried beforehulling121 Codex limit protectingparchment coffee(wet basis)< 12.54
Data table
Pointmoisture content, % as reported (basis not stated; Codex: wet basis)Source
Wet-hulled: wet parchment as stored before hulling (trial, North Sumatra)41.7–54.041.74–53.961
Wet-hulled: at wet hulling (Ismayadi et al., Mandheling trial)40–4540–451
Wet-hulled: at wet hulling, modified huller (FAO report)35–4535–452
Wet-hulled: at wet hulling, North Sumatran practice (FAO report)40–5040–502
Wet-hulled: optional intermediate holding (trial)17, held 3 weeks171
Wet-hulled: naked bean, final drying12121, 2
Fully washed control: parchment dried before hulling12121
Codex limit protecting parchment coffee (wet basis)< 12.512.54
Moisture at each step of the wet-hulled chain as reported in trials (basis not stated), against the fully washed control and the Codex limit for parchment coffee (wet basis).1,2,4

Moisture and mechanics of hulling#

In a fully washed chain the parchment comes off at about 12% moisture.1 In wet hulling it comes off at about 35–50%, roughly three to four times the moisture value.1,2 At that point the bean is soft and swollen rather than hard and glassy.7 A standard huller does not work on such coffee without changes: in the FAO project the steel huller bar was replaced by a rubber strip, and the machine was given more power and speed.2

The price of this is mechanical damage. Soft beans are crushed or split at the ends in the huller.7,12 In a Brazilian study of Arabica hulled after drying, mechanical damage from hulling lowered quality in storage for both natural and washed coffee.5 In the North Sumatran storage trial, the first visible mould was on naked and broken beans, in one lot on day 3.2

Drying without parchment#

After wet hulling, the bean dries with no parchment around it.2 Importers note that this leaves it exposed to swings in relative humidity and to contamination from dirt, debris and animals while it dries on tarpaulins.11 Some is dried on patios, on the road or on bare dirt.7,12 The Codex code of practice warns against both: bare soil is not appropriate for drying in rainy areas, and rewetting favours rapid fungal growth and OTA.4

Moulds and ochratoxin A#

The weakest point of the chain is the wet parchment waiting for the huller. In a 2004/05 trial in North Sumatra, six lots of wet parchment from farmers and collectors were stored for 1, 7 and 14 days in sacks before wet hulling.1,2 When mould became visible, the parchment was spread on a plastic sheet inside the warehouse.1

  • Mould. The FAO report states that infection clearly increased with storage time2; the journal abstract found no clear trend and points to differences between lots (see Contested).1 Black Aspergillus dominated; Aspergillus ochraceus was found at a low infection rate of 0–15.3%.1 Ochre-group fungi were found in 5 of the 6 lots stored for two weeks, and not at the shorter storage times.2
  • OTA. OTA was found only at low levels, below the European Union limit according to the journal report.1 Most of the positive samples came from parchment stored wet for 14 days.2 The exact counts differ between the two reports of the trial (see Contested).
  • Cup. Longer wet storage led to more musty flavours in the green coffee.2 Even so, the cup of many samples stored wet for up to two weeks was better than the authors expected.2

Chemistry and sensory studies#

Comparative chemistry is thin. No study opened for this entry measured sugars, acids, lipids or volatile compounds side by side in wet-hulled and fully washed coffee from the same lots. What exists is sensory:

  • In the North Sumatran trial, coffee stored wet for one day, hulled fast and dried fast to 12% was most likely to show the Mandheling character, and three of four tasters picked a sample of this kind as having the best Mandheling character.2 All tasters used the term “fruity/fermented”, which the report expected to be the easiest and commonest negative character to identify.2
  • Tasters also found some trial samples too clean in the cup, with less complex body and too green in colour compared with the traditional Mandheling they expected.2
  • In the Gayo highlands, beans were dried in two stages for wet hulling – partly before hulling, to a moisture within the range given by the North Sumatran reports, and again after it – or dried fully in one stage for dry hulling.3 Wet-hulled coffee scored better in the organoleptic test and was preferred.3

Open questions#

  • Where the flavour comes from. The authors of the Mandheling trial thought the handling probably contributes to the cup character1, but no source opened for this entry separates the effect of wet hulling itself from wet storage, fermentation, drying on the ground, and defects.
  • The seed’s own metabolism. Seed metabolism during processing affects sugars in washed coffee (see the washed process entry). No study opened for this entry follows the living seed through wet hulling, when the bean loses its parchment at high moisture.
  • Best moisture at hulling. The FAO and trial reports give about 35–50%1,2, and trade descriptions vary more widely, some well below that range.7,12 The trade-off between damage, drying time and mould has not been measured.
  • History. The sources opened for this entry do not give a primary, dated account of when wet hulling spread in Indonesia.

Key studies#

Ismayadi, Marsh & Clarke, 2005 – Wet storage before wet hulling. Stored wet parchment from six North Sumatran lots for 1, 7 and 14 days before wet hulling and compared it with a fully dried control. Black Aspergillus dominated, OTA stayed low, storage period showed no clear trend, and the best cup came from a lot stored wet for one day.

Pelita Perkebunan 21(2) · doi:10.22302/iccri.jur.pelitaperkebunan.v21i2.20

Marsh, FAO project report – The same trial in detail. The FAO/CFC/ICO project report gives the day-by-day protocol, the changes made to the huller for wet parchment, and the full mould, OTA and cupping results. It is the most detailed open description of how wet hulling is done.

FAO, Project GCP/INT/743/CFC, Annex E.6 · fao.org (PDF)

Abubakar, Karim & Fahlufi, 2011 – Wet vs dry hulling in Gayo. Compared Gayo Arabica varieties processed by wet hulling and by dry hulling. Wet-hulled coffee had lower acidity, stronger body and was preferred by the panel.

Proceedings, Annual International Conference, Syiah Kuala University (peer review not stated) · PDF

Abreu et al., 2023 – Hulling damage and storage. Studied how hulling and storage conditions affect green coffee quality. In Brazilian Arabica hulled after drying, mechanical damage from hulling, together with the loss of the fruit layers, lowered quality during storage – relevant to wet hulling, where the bean is hulled soft and then dried and stored naked, though wet hulling itself was not tested.

Anais da Academia Brasileira de Ciências 95(4) · doi:10.1590/0001-3765202320190612

Contested
  • Moisture at hulling: the journal report of a 2004/05 trial in North Sumatra describes hulling at 40–45%1, while the FAO report of the same project gives 35–45% for the modified huller and 40–50% for North Sumatran practice2; a trial in Gayo hulled at a moisture within the range of these reports.3 Trade descriptions disagree more widely: some describe further drying before the huller and give lower values7,12, others give values up to 50%.10,11 None of these reports states the moisture basis. No source opened for this entry tests which moisture gives the least damage or the best cup.
  • Mould and storage time in the Mandheling trial: the FAO project report states that mould infection clearly increased with the length of wet storage2, while the journal abstract of the same trial found no clear trend with storage period and attributes the variation mainly to differences between parchment lots.1
  • OTA results in the Mandheling storage trial: the journal abstract reports OTA in 5 of 42 samples at 0.17–2.24 ppb1, while the FAO project report of the same trial reports OTA in 7 samples at 0.07–2.24 ppb, four of them from parchment stored wet for 14 days.2 Both agree that all values were low.
  • Typical cup: the classic description is low acidity, heavy body and earthy, spicy flavour1,8; one importer describes a carefully processed wet-hulled lot with a vibrant, pineapple-like acidity.10 How far the classic profile comes from the process itself, and how far from defects such as mustiness, is not settled.2
Share or cite this entry

Sources

  1. AIsmayadi, C.; Marsh, A.; Clarke, R. (2005). Influence of Storage of Wet Arabica Parchment Prior to Wet Hulling on Moulds Development, Ochratoxin A Contamination, and Cup Quality of Mandheling Coffee. Pelita Perkebunan (Coffee and Cocoa Research Journal) 21(2). doi:10.22302/iccri.jur.pelitaperkebunan.v21i2.20 · other copies
  2. AMarsh, A. Storage of wet Arabica parchment prior to wet hulling including the storage of dry green bean coffee (Project GCP/INT/743/CFC, Annex E.6). FAO.
  3. BAbubakar, Y.; Karim, A.; Fahlufi, F. (2011). Flavor of arabica coffee grown in Gayo Plateau as affected by varieties and processing techniques. Proceedings of the Annual International Conference, Syiah Kuala University 1(1), 70–75.
  4. 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.
  5. AAbreu, G. F.; Rosa, S. D. V. F.; Coelho, S. V. B.; Pereira, C. C.; Malta, M. R.; Fantazzini, T. B.; Vilela, A. L. (2023). Influence of hulling and storage conditions on maintaining coffee quality. Anais da Academia Brasileira de Ciências 95(4). doi:10.1590/0001-3765202320190612 · other copies
  6. 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.
  7. BOwen, T. (2021). Sumatran Coffee Processing: Why You Should Know Giling Basah. Sweet Maria's Coffee Library.
  8. B(2019). Wet Hulled Process (glossary). Sweet Maria's Coffee Library.
  9. BFoster, D. (2019). The What, the How and the Why of Indonesian processing methods. Atlas Coffee Importers.
  10. BHaigh, T. (2024). What is Wet Hulled?. DRWakefield.
  11. BWet-Hulled (aka Semi-Washed, Sumatra Process, Giling Basah). Cafe Imports.
  12. CLynch, R. (2015). Indonesian Wet Hulled Coffee: Your One-Stop Guide. Perfect Daily Grind.

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”.

Suggest a change

On Wet-hulled (giling basah). Tell us what you would change and why. A source that supports it helps most.