The washed process, measured once
How does washed processing work?
Start the scene or choose a stage. The animation simplifies the mechanism; what follows gives the details and the available references.
The cherry is pinched between a drum and a breast plate set to tear off skin and flesh without crushing the seed. What comes out is parchment coffee coated in mucilage, a slimy layer that water alone does not remove.
Read the stages without animation
- Pulp on the day of harvestThe cherry is pinched between a drum and a breast plate set to tear off skin and flesh without crushing the seed. What comes out is parchment coffee coated in mucilage, a slimy layer that water alone does not remove.
- Ferment in a tank, a few dozen hoursIn this sugary medium, yeasts and lactic acid bacteria break down the pectin that holds the mucilage, and the pH falls from 6.0 to 6.5 toward 4.0: this acidification loosens the layer and keeps the undesirables at bay, as in a yogurt. In Yunnan, 36 to 48 hours after pulping, 12 hours after a mechanical demucilager. Dry, it is faster and hotter; under water, slower and buffered.
- Wash with plenty of waterThe water carries away the loosened mucilage and the coffee comes out as clean parchment. A 24-hour soak in clear water may follow: it tempers the effects of the fermentation that preceded it.
- Dry to under 12%The parchment coffee dries to under 12% moisture. The parchment stays: it leaves only at hulling, much later.
To remember: The drop in pH is the central event of the tank. The durations and the flora come from the Yunnan trials, the only complete published dataset: these values do not hold for all farms.
Read the full article and its sources ↓
The cherry is pulped on the day of harvest between a drum and a breast plate set to tear off the skin and flesh without crushing the seed. What comes out is coffee in parchment coated with a sticky layer, the mucilage, which water alone does not remove. It is left in a tank for a few dozen hours: yeasts and bacteria settle in this sugary medium, break down the pectin that holds the mucilage, and the layer comes loose.
It is washed with plenty of water, then dried. The only complete published data set on this sequence comes from trials in Yunnan, at 1,300 meters: on coffee that was simply pulped, standard fermentation lasts 36 to 48 hours, extended to 84; on coffee passed through a mechanical demucilager, 12 hours, extended to 72. The temperature of the mass starts at about 15 °C and drops to 11 to 13 °C. The pH starts at 6.0-6.5 and falls to about 4.0. The dominant flora is made up of lactic acid bacteria of the genus Leuconostoc (pseudomesenteroides, mesenteroides, holzapfelii), with Lactococcus lactis taking over in the demucilaged lots. Soaking 24 hours, drying to under 12%.
Zhang, De Bruyn, Pothakos, Contreras, Cai, Moccand, Weckx and De Vuyst, Frontiers in Microbiology 10:2621 (2019), solid level| Washed process, Yunnan 2019 | Value |
|---|---|
| Fermentation, pulped | 36-48 h, extended 84 h |
| Fermentation, demucilaged | 12 h, extended 72 h |
| Temperature of the mass | 15 °C → 11-13 °C |
| pH | 6,0-6,5 → 4,0 |
| Soaking | 24 h |
| Drying | below 12% moisture |
The drop in pH from 6.5 to 4.0 is the central event in the tank: the medium acidifies because the microorganisms make organic acids, and this acidification is both what loosens the mucilage and what keeps undesirable organisms from settling in, exactly as in yogurt. A fermentation that does not acidify is a fermentation that drifts. The sensory effects are measured, not told: extended fermentation increases fruitiness and acidity and decreases cereal and floral notes; pulping, compared with demucilaging, gives more fruitiness and less humus and earthiness; the final 24-hour soak increases overall intensity, decreases spiciness, and tempers the effects of the fermentation that preceded it. One step can therefore erase part of the work of the step before.
Zhang et al. 2019; LC ch. 17bFermentation can be run dry or under water. Dry, in an open tank, with the mucilage alone, it is faster and hotter, because nothing carries away the heat that the microorganisms release; under water, it is slower and thermally buffered. The range of 12 to 18 hours cited for the underwater version comes from non-institutional Colombian relays. As for the rule “the higher and cooler, the longer the fermentation,” it is consistent with what is known about the effect of temperature on microbial activity, universally taught, and no study quantifies it: the Yunnan trials are single-altitude.
LC ch. 17b, from the external research of August 12, 2026; no published duration/altitude curve