Processing

What you will be able to do

• Describe the washed, natural, honey and wet-hulled processes step by step
• Explain what fermentation is doing and why it must be controlled
• Explain why drying is the riskiest stage
• Describe what 'anaerobic' and 'carbonic maceration' mean on a label
• Separate the usual flavour tendencies of a process from a guarantee

Assumes: Level 4: World coffee.

Three main routes from cherry to dry seed

From published standards or research

Processing has one job: to get from a wet, sugary fruit to a stable, dry seed without rot or mould. The methods differ in when the fruit is removed.

In the washed process, the skin and pulp are stripped off mechanically soon after picking. The sticky mucilage that remains is broken down by fermentation in tanks, usually for a day or two, and then washed away, or removed mechanically. The seed is dried in its parchment. Because the fruit is gone early, the result is generally described as clean and clear, with the coffee's acidity prominent.

In the natural or dry process, the whole cherry is dried intact, like a raisin, and the dried fruit is hulled off afterwards. It is the oldest method and needs little water. The seed spends weeks in contact with fermenting fruit, and naturals are generally described as fruitier, sweeter and heavier, sometimes winey.

Between them sits the honey or pulped natural process: the skin is removed but some or all of the mucilage is left on during drying. The names 'white', 'yellow', 'red' and 'black' honey loosely indicate how much mucilage was left and how slowly it dried. The cups tend to fall between washed and natural.

In more depth: Washed · Natural · Honey · Pulped natural

Wet hulling

From published standards or research

Wet hulling, known in Indonesia as giling basah, is a regional method that produces a recognisable style. The coffee is pulped and briefly fermented as in the washed process, but then the parchment is hulled off while the seed is still very moist, and the bare seed finishes drying unprotected. The method suits a humid climate where drying in parchment is slow.

The result is the low-acid, heavy, earthy or herbal profile widely associated with Sumatra. It is a clear case of a flavour attributed to a place that belongs largely to a process.

In more depth: Wet-hulled processing · Aceh, Sumatra

Fermentation and the experimental methods

CoffeeHQ explanation of the mechanism

Fermentation happens in every process, whether intended or not. Yeasts and bacteria that live on the fruit and in the environment consume the sugars in the mucilage. In the washed process this is used to loosen the mucilage. In naturals it happens inside the drying cherry. The microbes also produce acids, alcohols and other compounds, some of which pass into the seed and shape flavour.

Controlled, it adds complexity. Uncontrolled, it produces defects: vinegar-like sourness, a rotting or 'ferment' taste, or a medicinal note. The variables are the familiar ones of any fermentation — time, temperature, how much oxygen is present and which organisms dominate.

The methods sold as experimental are attempts to steer those variables. 'Anaerobic' means fermenting in a sealed vessel with oxygen excluded. 'Carbonic maceration', a term borrowed from winemaking, means fermenting whole cherries in a vessel flushed with carbon dioxide. Some producers add selected yeasts, and some ferment with added fruit or other material, which is usually called co-fermentation and is controversial, because it blurs the line between a coffee's own flavour and an added one. These terms are not regulated and are used loosely; how the result tastes varies enormously from producer to producer.

In more depth: Anaerobic fermentation · Carbonic maceration · Winey and fermented flavours

Drying

From published standards or research

Whatever came before, the coffee must be dried to a moisture content of roughly ten to twelve per cent to be stable for storage and export. Too wet and it moulds; dried too fast or too hot and the seed is damaged and ages badly; dried unevenly and the lot is inconsistent.

Coffee is dried on patios, on raised mesh beds that let air circulate underneath, or in mechanical dryers, and is turned regularly. Slow, even drying is widely regarded as better for both flavour and how long the green coffee keeps. It is unglamorous work, and it is where many otherwise good coffees are lost.

In more depth: Coffee production, stage by stage

Practise with a tool

Exercise: Washed beside natural

See all practical exercises

Work it through: Is this coffee off?

A customer returns a bag labelled 'anaerobic natural', saying it smells of overripe fruit and rum and tastes almost alcoholic. They ask whether it has gone bad.

Reasoning it out

1. The label describes a long, oxygen-free fermentation of whole fruit, which is designed to produce intense fermented-fruit character.
2. Boozy, tropical and winey notes are the intended result of that method, not spoilage after roasting.
3. Whether that intensity is pleasant is a matter of preference, and of how well the fermentation was controlled.
4. A true defect would be more like vinegar, rot or a medicinal taste.

What to do

The coffee is very likely as the producer intended. The honest answer is that this style divides people, and that 'washed' is the word to look for if they want the opposite. If it tastes of vinegar rather than fruit, that is over-fermentation and a fair complaint.

Anaerobic fermentation

Check yourself

Answer in your head first. Nothing is scored and nothing you open here is recorded.

1. 1. In which process is the whole cherry dried intact?

   • Washed
   • Natural
   • Honey
   Show the answer

   Natural.

   The fruit is removed only after drying, so the seed is in contact with it throughout.

   Back to “Three main routes from cherry to dry seed”

2. 2. What does fermentation do in the washed process?

   Show the answer

   It breaks down the mucilage so it can be washed off the parchment.

   It also contributes to flavour, which is why its length and conditions matter.

   Back to “Fermentation and the experimental methods”

3. 3. What makes wet hulling different from the washed process?

   Show the answer

   The parchment is removed while the seed is still moist, and the bare seed finishes drying.

   This is the source of the heavy, earthy Sumatran style.

   Back to “Wet hulling”

4. 4. True or false: natural coffees always taste fruitier than washed coffees.

   Show the answer

   False.

   It is a common tendency. Careful drying can give a very clean natural, and long fermentation a very fruity washed coffee.

   Back to “Three main routes from cherry to dry seed”

Comparisons worth making now

• Washed or natural processThe central comparison in processing, with the limits of the generalisation set out.

Reference for this level

• All processing methods
• Thermal shock
• Cascara
• Coffee waste and by-products

Where the facts in this level come from

• World Coffee Research variety and agronomy resources — World Coffee Research (WCR)
• The World Atlas of Coffee, James Hoffmann
• SCA green coffee grading protocol and defect classification — Specialty Coffee Association

Sections are labelled with the kind of claim they make. How CoffeeHQ uses sources, and what each one is relied on for, is set out in the source and evidence policy.