The way a coffee is processed after harvesting can have a dramatic effect on the resulting cup. As such, it has been an increasingly important part of how coffee is described and sold. But coffee producers almost certainly don’t have a flavor in mind when they select a processing method (though some do). For most producers the goal is to ensure the processing causes the least possible incidence of defect and causes no drop in the quality, and thus, monetary value.

After harvest, coffee cherries are taken to a wet mill to separate the beans from the flesh, and dry the beans so they are safe for storage. (If too much moisture is retained, the coffee could rot while waiting to be sold and shipped.) A wet mill can be anything from a small collection of equipment on an individual farm, to a very large industrialized facility for processing huge amounts of coffee.

The wet mill processes coffee from the cherry stage on to the parchment stage, which is when the bean is dry but still covered with its layer of parchment. Most people believe the coffee is pretty well protected by this layer, and that it doesn’t begin to degrade until the coffee is hulled to remove the parchment at the last possible moment before the coffee ships.

Natural Process

Also referred to as “dry process,” this is the oldest method of processing coffee. After harvest, the coffee cherries are spread out in a thin layer to dry in the sun. Some producers spread them out on brick patios, other use special raised drying tables, which allow for better airflow around the cherry (resulting in more even drying). The cherries must be turned regularly to avoid mold, fermentation or rotting. Once dried, the outer husk of skin and dried fruit are removed mechanically, and the raw coffee is then stored before export.

This process adds certain flavors to the coffee, which are sometimes desired, but often quite unpleasant. If there is little access to water, though, the producer may have no other option. For that reason, the natural process is common in Ethiopia, and in parts of Brazil. Worldwide, natural processed coffees are often viewed as inferior, and the majority of coffee produced this way is cheap and low-quality. However, there are those who choose this method to process high-quality coffee, and they often find the process to be more expensive due to the additional labor involved in the attentive, careful drying of the cherries.

Good natural processed coffee can impart greater fruit flavors, regardless of variety and terroir. These are often described as blueberry, strawberry or tropical fruit. This process can be somewhat unpredictable, and even a high-quality lot could be irreparably damaged.

Washed Process

The goal of the washed process is to remove all of the sticky flesh from the coffee seed before it is dried. This greatly reduces the chance of something going wrong during drying, so the coffee is likely to be worth more. However, this process is much more expensive than others.

After picking, the coffee cherry has its outer skin and most of the fruit flesh stripped off using a machine called a depulper. The coffee is then moved to a clean tank or trough of water where the remainder of the flesh is removed by fermentation. The fruit flesh contains a lot of pectin and it is firmly attached to the seed, but the fermentation breaks down the remaining flesh enough for it to be washed away. Different producers use different amounts of water during the fermentation stage, and there are some environmental concerns about this method (mostly due to waste water, which can be toxic).

The amount of time that fermentation takes can depend on several factors, including the altitude and ambient temperature. The hotter it is, the faster this process will occur. if the coffee is left too long to ferment then negative flavors can creep in. After fermentation, the coffee is washed to remove the leftover debris, then it is ready to be dried. This is usually done in the sun by spreading out the coffee on brick patios or raised drying tables. In the same way as the natural process, the coffee must be turned regularly with large rakes to ensure slow and even drying.

In places with a lack of sunshine or excess humidity, produces sometimes use mechanical dryers to dry the beans down to a suitable moisture content (11-12 percent). In terms of cup quality, mechanical drying is often considered inferior to sun drying.

Compared to other processes, washed process coffee tend to present a higher level of acidity, increased complexity and what is described as a cleaner cup. “Cleanliness” is an important term used in coffee to indicate the absence of any negative flavors, such as off tastes or unusual harshness and astringency.

Hybrid Process

Pulped Natural Process

Mainly used in Brazil, this process is the result of experiments run by a coffee-processing equipment manufacturer called Pinhalense. The idea was to process coffees with high cup quality using less water than that used in the washed process.

After picking, the coffee is mechanically depulped, stripping all of the skin and much of the fruit flesh from the beans. From there it goes straight out to dry on patios or drying tables. With less flesh surrounding the beans there is a decreased risk of defect, yet there is still enough sugar in the surrounding fruit to see a noticeable increase in sweetness and body in the coffee. This process still requires careful drying after depulping.

Honey (Miel) Process

This process is very similar to the pulped natural process but used in a number of Central American countries, notably Costa Rica and El Salvador. The coffee is mechanically depulped, but the method uses even less water than the pulped natural process. The depulping machines can usually be controlled to leave a specific percentage of the flesh on the beans. The resulting coffee is then referred to as one hundred percent honey or twenty percent honey, for instance. With larger quantities of flesh being left on the beans, there is a higher risk of fermentation and defect when the coffee is dried.

Semi-Washed/Wet-Hulled Process

This process is common in Indonesia, where it is known as giling basah. After picking, the coffee is depulped and then briefly dried. Instead of drying the coffee to a moisture content of 11-12 percent, as other processes do, the coffee is only dried to 30-35 percent. It is then hulled, stripping off the parchment and exposing the green coffee beans beneath. The naked beans are then dried again until they are dry enough to be stored without the risk of rotting. This second drying gives the beans a distinctive deep swamp-green color.

The semi-washed process is the one exception to the practice of keeping the parchment on the beans until just before shipping. it is considered by many to result in a form or defect, but the market has come to associate the flavors with coffees from Indonesia, and therefore does not demand an end to the practice. Semi-washed coffees have lower acidity and more body than other coffees, and the process also creates a number of different flavors such as wood, earthy, mustiness, spice, tobacco and leather. There is strong disagreement within the industry over whether or not this is desirable. many feel that these flavors dominate the flavor of the coffee, and we rarely get to find out how coffees from Indonesia really tastes.