Sumatran coffee tastes the way it does because of when the parchment comes off. In the wet-hulling method Indonesians call giling basah, the parchment layer is removed while the bean is still at 40 to 45 per cent moisture, instead of after drying to about 12 per cent as everywhere else. That description, and the moisture figures, come from a study by the Indonesian Coffee and Cocoa Research Institute’s own journal, which sets out the whole sequence: “following de-pulping and 1-2 days sundrying, wet parchment is stored for varying periods up to a few weeks, the parchments are then de-hulled when still wet (40-45% moisture content) then the beans sundried.”
The same paper describes the resulting cup without any help from us: Mandheling coffee “is characterised by low acidity, heavy-complex body, spicy-little earthy and fruity flavor”, produced “by smallholder farmers in the highland surrounding Lake Toba North Sumatra”. Note the paper’s own hedge, which we are keeping: the handling procedure “presumably contributes to the unique cup character”. Nobody has proved the causal chain; the association is long-observed and the method is genuinely unusual.
Table of Contents
What an earlier version of this page got wrong
The moisture figure was too low, and it was stated twice. The page said the parchment is hulled “when the moisture content reaches around 30%-40%”, in the body and again in the FAQ block. The Indonesian Coffee and Cocoa Research Institute study puts the practice at 40 to 45 per cent, and the wet parchments it actually sampled from farmers and collectors in the region measured 41.74 to 53.96 per cent moisture. The method is wetter than the page said, which matters, because the whole point of it is how far it departs from normal practice.
The source for giling basah was a YouTube video. The word was linked to a video rather than to any study or industry document. It is now linked to the paper.
Three tasting-note tables have been removed. Sumatra as “earthy, spicy, herbaceous”, Java as “sweet herbal notes, full-bodied”, Sulawesi as “bold, dark chocolate, ripe fruit, subtle earthiness”, plus a variety table giving Kopi Luwak “smooth, rich, less acidic” and Mandheling “hints of chocolate and tropical fruit”. Nobody at this site has cupped any of these coffees. The one cup description on this page now is quoted from a published study and attributed to it.
Kopi luwak was described twice in appealing terms and qualified only in passing. The page said the civet’s “digestive enzymes alter the structure of the coffee beans, resulting in a smoother and less acidic brew” and that the process produces “a coffee that’s smooth, rich, and less acidic”, with no source for either claim, followed by a single sentence about “questionable animal welfare practices”. That balance is the wrong way round, and the section below replaces it.
The FAQ block and the closing “Conclusion” section are gone, and their one piece of genuine content — the processing answer — is in the opening paragraphs where it belongs.
What wet hulling actually does, and the risk that comes with it
Normal processing dries parchment coffee down to around 12 per cent moisture before hulling. Indonesia’s own national standard for green coffee beans, SNI 01-2907-2008, sets 12 per cent as the reference moisture content, and researchers working on Gayo arabica hold their samples there for exactly that reason. Wet hulling breaks that sequence: the bean is stripped of its parchment while still soft and swollen, then dried naked in the sun. Handling green coffee at 40 per cent moisture is what gives wet-hulled beans their unusual physical appearance and, the trade holds, their heavy body and low acidity.
Storing wet parchment for days or weeks before hulling has an obvious hazard, and the study measured it rather than speculating. Its design used the normal wet process, dried thoroughly to 12 per cent, as the control, and stored wet parchment in polyethylene sacks for 1, 7 and 14 days. The findings were mixed and are worth reporting in full rather than selectively:
- Moulds did grow. “black Aspergillus was the dominant species found in the beans, while A. ochraceus an OTA producer, was found in some samples with low infection rate (0-15.3%)” — the missing comma is the paper’s own.
- The toxin mostly did not follow. “OTA was found in only 5 samples out of 42 samples with range of 0.17-2.24 ppb, very less than European Union limit.”
- Length of storage did not predict the outcome. “There was no clear trend of storage period on the mould infection rates, OTA content, and the Mandheling cup characters”, which the authors attribute to the variability of the farmer lots they used.
- The existing local practice helps. “Spreading of coffee inside the warehouse during the day could suppress moulds growth.”
So the honest summary is: wet hulling creates a real mould pathway, and in this trial it did not translate into ochratoxin A above European limits. One trial on six lots is not a food-safety clearance for an entire origin, and we are not presenting it as one.
One claim we could not source: wet-hulled green beans are frequently said to have a distinctive blue-green cast. It is repeated throughout the trade and it may well be right, but we did not find it in any study or standard we opened, so this page does not assert it.
Indonesia is a robusta country with a famous arabica sideline
This is the piece of context the old page never gave. On the USDA Foreign Agricultural Service forecast for 2026/27, Indonesia produces 11.38 million 60-kg bags — 10.0 million of it robusta and 1.38 million arabica. Roughly seven bags in eight are robusta, Coffea canephora. The Sumatran arabica that carries the country’s reputation abroad is a small fraction of what the country actually grows.
| Indonesia, thousand 60-kg bags | 2021/22 | 2024/25 | 2026/27 forecast |
|---|---|---|---|
| Robusta | 9,300 | 9,300 | 10,000 |
| Arabica | 1,280 | 1,400 | 1,380 |
| Total | 10,580 | 10,700 | 11,380 |
From USDA FAS, Coffee: World Markets and Trade, July 2026. The geography of the crop is lowland, not highland: production is forecast down 1.0 million bags because “excessive rainfall disrupted flowering and cherry formation in the lowland areas of Southern Sumatra and Java, where approximately 75 percent is grown”. Gayo in Aceh, Lintong and the Mandheling highlands sit above all that, and are where the wet-hulled arabica comes from.
Kopi luwak: what the research says, honestly
Civet coffee is the thing about Indonesian coffee that most readers arrive already knowing, so it should be handled properly rather than sold.
The animal welfare evidence is specific, recent and bad. Lewis-Whelan and colleagues assessed 29 civet coffee tourism plantations in Bali and eight wildlife markets that supply them, publishing in the Journal of Applied Animal Welfare Science in 2024. They “found 99 civets in civet coffee tourism plantations and 136 in markets”, estimated that “annually between 400 and 800 civets are sold”, and reported flatly that “welfare standards do not meet the Indonesian laws and regulations” and that “no civet met all of the five freedoms”. Diet, hygiene, water availability and mobility all affected the animals’ body condition scores. Their recommendation is that tourists “should be made aware of the low welfare standards to inform their choice about supporting this industry”.
Much of what is sold as kopi luwak is not kopi luwak. Adulteration is a well-enough recognised problem that analytical chemists have built methods to detect it — Suhandy and Yulia published a UV-visible spectroscopy and partial-least-squares approach in the International Journal of Food Science in 2017 specifically “to protect the authenticity of luwak coffee and protect consumer from luwak coffee adulteration”. Earlier metabolomics work by Jumhawan and colleagues did the same job with discriminant markers. Nobody builds an authentication method for a product that is not being faked.
A widely repeated figure says 42 per cent of kopi luwak is fake or adulterated. It appears in a 2021 commentary in Foods by Lachenmeier and Schwarz, who write that “it is almost a relief that much coffee labelled as Kopi Luwak is probably a counterfeited product that has never seen the digestive tract of an animal”, and put the 42 per cent in brackets as a claim. We followed their citation: it leads to a 2007 report by National Public Radio, not to a study. Treat the general point as sound and the specific percentage as unmeasured.
That same commentary makes a taxonomic argument worth flagging: examining bean shapes in the published photographs of “digested” coffees, the authors conclude that “the actual coffee species under investigation has been Coffea liberica, not Coffea arabica or Coffea canephora, which has been incorrectly assumed”. If they are right, some of the chemistry literature on kopi luwak has been comparing the wrong species. Our page on liberica covers that species, including the 2025 genomic work by Davis and colleagues that split it into three — C. liberica, C. dewevrei (excelsa) and C. klainei.
We are not recommending kopi luwak and we do not link to sellers of it.
Kopi tubruk, and the rest of the archipelago
Two things the old page got right and are kept. Kopi tubruk is a real and specific preparation — grounds boiled with sugar and served unfiltered, with the grounds settling in the cup — and street coffee stalls, warung kopi, are a genuine part of daily life rather than a travel-brochure flourish. Java’s name became a synonym for coffee because Dutch cultivation started there. Sulawesi’s Toraja highlands use wet hulling too, which is why Sulawesi and Sumatra are so often described in similar terms.
For the species themselves, see our pages on arabica and robusta; for how a warming climate is expected to redraw the growing map in Southeast Asia, see climate change and coffee farming.
Sources
- “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 (a Coffee and Cocoa Research Journal) 21(2), 2005, published by the Indonesian Coffee and Cocoa Research Institute.
- Lewis-Whelan, Ardiansyah, Roberts, Nijman, Damianou, Morcatty, Birot, Imron and Nekaris, “Welfare and Management of Civets in Civet Coffee Tourism Plantations”, Journal of Applied Animal Welfare Science 27(3), 2024, 561-574.
- Suhandy and Yulia, “The Use of Partial Least Square Regression and Spectral Data in UV-Visible Region for Quantification of Adulteration in Indonesian Palm Civet Coffee”, International Journal of Food Science, 2017.
- Lachenmeier and Schwarz, “Digested Civet Coffee Beans (Kopi Luwak) – An Unfortunate Trend in Specialty Coffee Caused by Mislabeling of Coffea liberica?”, Foods 10(6):1329, 2021.
- Yulia, Analianasari and colleagues, “The Authentication of Gayo Arabica Green Coffee Beans with Different Cherry Processing Methods”, Foods 12(23):4302, 2023 — source for the SNI 01-2907-2008 reference moisture content.
- USDA Foreign Agricultural Service, Coffee: World Markets and Trade, July 2026.
