Processing Coffee

From cherry to parchment

Processing Coffee

How a coffee is processed after harvest can have a dramatic effect on the final cup, which is why processing has become such an important part of how coffee is described and sold. Yet we should resist the romantic assumption that producers usually choose a process because they are chasing an ideal flavour profile. A few certainly do. Most are trying first to protect value by limiting defect and preventing unnecessary loss in quality.

After harvest, cherries are taken to a wet mill, where the seeds are separated from the fruit and dried until they are safe for storage. Fresh coffee may begin with a moisture content of around sixty per cent, but it typically needs to be reduced to roughly eleven or twelve per cent if it is to survive waiting, shipping, and sale without rotting. A wet mill may be nothing more than a small farm installation, or it may be a large industrial facility processing enormous volumes of coffee.

The wet mill moves coffee from the cherry stage to the parchment stage, when the seed is dry but still protected by its outer parchment layer, often called pergamino. Many in coffee believe that this layer helps preserve quality until hulling takes place close to export. The phrase wet milling is slightly misleading, because some methods use very little water at all. It remains useful mainly because it distinguishes this early stage from dry milling, when the parchment is removed and the coffee is graded. Processing, then, is not just technique. It is one of the producer's most consequential economic decisions.

Quick comparison

Processing Methods — At a Glance

Dry process

The Natural Process

Also known as the dry process, the natural method is the oldest way of processing coffee. After harvest, whole cherries are spread out in a thin layer to dry in the sun. Some producers use brick patios, while others use raised drying beds that allow better airflow and therefore more even drying. However the surface is built, the principle is the same: the cherries must be turned regularly so that mould, fermentation, and rot do not take hold.

Once the coffee is fully dry, the outer husk of skin and dried fruit is removed mechanically, and the raw coffee is then stored before export. Where water is scarce, this may be the most practical method available, which helps explain its long presence in places such as Ethiopia and parts of Brazil.

The natural process can produce remarkable coffees, but it is an unforgiving one. It often adds fruit-heavy flavours to the cup, sometimes beautifully and sometimes clumsily. Notes described as blueberry, strawberry, or tropical fruit may appear in a successful lot; in a poor one, the language turns quickly toward barnyard, ferment, wildness, or manure. For this reason naturals often divide opinion. Their admirers see them as evidence of coffee's extraordinary flavour range. Their critics see them as risky, unstable, and potentially dangerous to producer income when drying goes wrong.

Stability over time

Drying Speed and Storage Potential

There is growing evidence that slow and even drying may improve not only short-term cup quality but also the way a coffee ages in storage. Coffees dried too quickly can lose their attractive qualities surprisingly soon after arriving at the roastery, in some cases within only weeks or months.

That matters because green coffee is expected to travel and rest before it is roasted. If rushed drying shortens the stable life of the coffee, the producer, roaster, and consumer all inherit the consequence of that impatience.

Cleanliness and control

The Washed Process

The goal of the washed process is to remove all of the sticky fruit from the coffee seed before it is dried. After picking, the cherry first has its skin and most of its flesh stripped away by a depulper. The coffee is then moved into a tank or channel where fermentation breaks down the remaining pectin-rich mucilage so that it can be washed away.

This greatly reduces the chance that drying will go wrong, which is one reason washed coffees are often worth more. It is, however, a more expensive process than the alternatives, and it usually demands more water. Producers must also judge fermentation carefully. The time required depends on temperature, altitude, and local conditions, and if the coffee is left too long, unwanted flavours begin to creep in.

After fermentation, the coffee is washed clean and dried, often on patios or raised beds, though some producers rely on mechanical dryers where sunshine is unreliable or humidity is too high. At its best, the washed process tends to produce coffees with greater acidity, more distinct flavour separation, and what professionals call a cleaner cup. Cleanliness here means the absence of off-flavours, harshness, and distracting astringency, not the absence of character.

Between natural and washed

Hybrid Processes

Between the natural and washed poles sits a family of hybrid processes. These methods try to reduce some of the risk of drying whole cherry while still preserving some of the sweetness, body, and textural character that come from leaving fruit around the seed for longer.

Their attraction is practical as much as sensory. They allow producers to balance climate, labour, equipment, and water use while still shaping the flavour profile of the coffee in a deliberate way.

Size and roasting behaviour

Grading of Coffee

Coffee has been graded by size for longer than it has been graded by quality, and in many places the two ideas are still treated as though they were naturally the same. They are not. Grading is usually done with sieves whose numbers indicate the size of the perforations through which the beans can pass.

Peaberry is one specialized grade based on the small, rounded beans that occur when a cherry develops only one seed instead of two. Some regard peaberries as especially intense or desirable, though that belief is not universally accepted. More broadly, the advantage of a narrow size range is practical rather than romantic: it helps the roaster produce a more even roast.

Beans of different sizes and densities roast at different speeds. In a mixed batch, smaller or less dense beans may race ahead while larger or denser ones lag behind. What grading offers, at its best, is not proof of excellence but a better chance of consistency.

Grading of Coffee — Regional terminology

Common Size Grades

Different producing regions developed their own names for size grades. In Colombia, Supremo and Excelso are among the best known, with Excelso referring to smaller screen sizes and Supremo to larger ones. In parts of Central America, larger sizes have historically been marketed as Superior, while peaberries are often called caracol.

Across parts of Africa, especially Kenya, one commonly encounters AA, AB, and A, with AA traditionally treated as the largest screen size. These systems matter not because size automatically guarantees quality, but because the trade has long used visible size as a language of value, whether or not the cup entirely deserves the promise.

Quality control

Defining Defect

The term defect has a fairly specific meaning in coffee. It refers to beans or lots that have developed problems serious enough to create bad flavours and reduce commercial value. Some defects are visible in the raw coffee, as when a bean has been damaged by insects. Others reveal themselves only when the coffee is roasted and tasted.

A mild defect may simply reduce elegance. A more serious fault can make the coffee taste harshly phenolic, metallic, or even sulphurous. Poor processing can also push a lot toward unpleasant fermentation, giving the cup a dirty, boozy, barnyard-like, or rotten-fruit character. These are not charming irregularities. They are signs that something went wrong in the chain from harvest to storage.