After a coffee cherry is picked from the tree, its perilous journey along the path to quality hits an important crossroads. Coffee’s inherent quality is close to its peak during this initial duration of time once it is picked, and the choice in how a coffee bean will be processed is one that is meant to truly showcase the inherent quality of the bean or compliment those raw attributes in a positive way. Coffee is processed differently throughout the world; sometimes this is due to legacy or tradition without an understanding of its influence on the cup, while other times it is a specific choice at the farm level to add or coax out new flavors and experiences in the profile of the coffee.
Coffee processing methods
Within countries, and even within specific farms, several processes can be done. Producers around the world are experimenting with new processing techniques and styles everyday.
There are several major categories of coffee processing recognized by the coffee industry as a whole. Sometimes these are called different things depending on what country you are in, but the general principles remain the same. Below you will find some information on the main processing techniques used around the world: fully washed, natural, pulped natural, and wet hulled.
1. Wet / Washed Process
A coffee processing method which involves “washing” the green coffee beans to remove the coffee’s fruity material while the coffee cherry is still moist (e.g., just after picking).
Characteristics of a Wet Processed Coffee
Washed coffee is distinguished by the clarity of the flavors and attributes that it can achieve. This clarity need not suggest timidity, as the best washed coffees combine nuance and complexity with great intensity. Clarity should also not be regarded merely as simplicity. Rather, it is exactly the transparency of wet processed coffees that allows for perception of the remarkable complexity of acids and other compounds present in the coffee beverage- complexity that is frequently masked in alternately processed coffees.
During this process, the sugars present in the mucilage are removed through natural fermentation or mechanical scrubbing. Fermentation can be done by stacking the coffee outside or placing them under water and allowing nature to take its course. After the sugars are removed, the beans then can be taken through a secondary washing to remove any additional debris, or taken immediately to the patios or beds for drying.
Pulping and Fermentation
During wet processing, the pulp (i.e.the exocarp and a part of the mesocarp) is removed mechanically. The remaining mesocarp, called mucilage, sticks to the parchment and is also removed before drying. Hulling of dry parchment coffee leads to green coffee. The wet process is used for most Arabicas… and only for a small percentage of Robustas, although the trend to wet process Robustas is increasing.
Mucilage is insoluble in water and clings to parchment too strongly to be removed by simple washing. Mucilage can be removed by fermentation followed by washing or by strong friction in machines called mucilage removers. Fermentation may be natural or accelerated by chemicals or enzymes. Mechanical mucilage removers operate by rubbing parchment beans against each other and against the mobile and static parts of the machines.
Rinsing and Sun-Drying the Coffee Beans
After the coffee beans are washed (flushed) again with clean, fresh water they are dried either out in the open or in large, heated rotating cylinders in mechanical dryers. Sun drying is preferred in climates with predictable sun and weather patterns, as it requires no investment in mechanical equipment. The downside that has to be factored in is rain, so climates with consistent seasons that don’t rain at certain times are more ideal than others.
2. Natural / Sundried / Dry Processed
Dry processing is a type of coffee processing that involves drying the freshly-picked coffee cherry (fruit) in the sun on large patios for a period of time while repeatedly raking and turning the drying cherry until the green coffee beans are generally free of any dried fruit and the moisture content is about 10.5%. Mechanical dryers may be used instead of sun-drying.
While the coffees gain unique flavors through this process, it’s also a risky bet – a minimum of 2 weeks without sun is needed to allow for drying. Rain or high humidity leads to the develop of molds and fungus and can ruin a harvest – sometimes a farmer’s entire income.
Characteristics of a Dry processing
Natural coffees frequently carry a flavor similar to that of the coffee cherry itself. While this flavor profile is a limiting factor in scoring washed coffee, it is characteristic of the dry process and as such is assessed for its relative quality and integration in the coffee beverage. At its most simple, Naturally processed coffee is coffee that is dried with the cherry remaining on the bean and parchment throughout the drying process and will often remain on until just before the time of export. Naturally processed coffee can be categorized as “special prep”, meaning ripe cherries are picked and dried, or it can be coffee cherries that dried on the tree and finished on the patios or drying beds.
Many coffee connoisseurs consider wet-processed coffees superior to dry unwashed (dry-processed; natural) coffee, but this is clearly a matter of personal preference. The dry process is used for more than 80% of Brazilian, Ethiopian and Yemen Arabicas, and for almost all Robusta coffees in the world.
3. Pulped Natural / Semi-dry / Honey Process
Pulped Natural processing is a method that removes the outer skin of the coffee cherry to expose the fruity layer, and is then allowed to dry in the sun (or sometimes, with mechanical dryers). It’s considered to be half way between dry processing and wet processing – it requires more processing time and consumes more water than straight natural processing, but also offers a better quality cup.
Pulping the Coffee to Remove the Outer Skin
Often used in Brazil where strip-picking is the norm, the pulped natural processing method involves first pulping the coffee to remove the outer skin, though this is done without the fermentation stage. The coffee cherry is then sun-dried, with much of the mucilage still attached, on a raised drying bed or on a patio.
Outside of Brazil the pulped natural process is frequently referred to as the honey process, with producers leaving various amounts of mucilage adhering to the parchment as well as employing different depths of the coffee layer in drying, both resulting in unique profiles that span and even expand the range from dry to wet process.
Characteristics of Coffee with Pulped Natural Processing
There can also be varying levels of honey processed coffee, typically referred to as black, red, or yellow honey. This is where it gets a bit complicated. In some regions, the level of honey is determined by the frequency of turning the parchment while drying, with the black end of the spectrum being turned least often. Not turning the coffee often allows the sugars to caramelize quickly on the outside of the parchment, leaving it stained a dark maroon or “black” color.
In other places, the degree of honey is determined by the amount of mucilage left on the parchment after being passed through a mechanical demucilaginator or quick fermentation. In this scenario, the black end of the spectrum has the most mucilage left on, while the yellow has the least. There are no hard and fast rules with terminology for honeys as there is currently no global processing standards (one day?!), but having this basic understanding will be a great start.
Pulped Natural processing is done to bring out the natural sweetness and aromatics of coffee – it will lead to a better tasting coffee if done properly.
Wet Hulled/Semi-washed/Giling Basah
The assessment of wet hulled coffees is challenging, to say the least. The potential range of coffee flavors, process flavors and environmentally imparted off flavors is dramatic. In general these coffees occupy a range from earthy to vegetative. Scoring relies heavily on discerning between sweeter and “cleaner” (e.g.. clean earth vs compost or roasted pepper vs raw) versions of each. Despite the frequent assertion that wet hulled coffees are low acid, we’ve found that carefully processed coffees can display significant and vibrant fruit acidity, integrated with the wilder flavors imparted by the process itself.
Regions Where Semi-washed Processing is Used
Most small-scale farmers on Sulawesi, Sumatra, Flores, and Papua use a unique process, called “Giling Basah”, which literally means “wet grinding” in Bahasa Indonesia. The industry also uses the terms wet hulling, semi washed and semi dried for this method. To avoid confusion, SCAI is encouraging the term Giling basah.
Demucilaging in the Giling Basah Method
In this technique, the outer skin is removed from the cherries mechanically, using rustic pulping machines, called “Luwak”. The coffee beans, still coated with mucilage, are then stored for up to a day. Following this waiting period, the mucilage is washed off and the coffee is partially dried for sale (to 30% to 35% moisture).
Processors then hull the coffee in a semi-wet state, which gives the beans a unique bluish green appearance. This process reduces acidity and increases body, resulting in the classic Indonesian cup profile. (SCAI)