Coffee Processing Primer: Differentiation and Value-Added Distinction

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By Kim Westerman

The aromas and flavors of coffee are influenced by a variety of factors, including varietal, ripeness, and fermentation at the farm level — even coffee in the bulk bins on grocery shelves and vacuum-sealed tins from big-name brands are now often labeled with details about a coffee’s precise origin. Third-wave roasters drill down to listing farmers’ names, elevation of farms, and names of specific microlots. At the roastery/café, roast level and brewing method are the decisive factors that influence cup profile. But even more influential on the final outcome of an individual coffee is its processing method.

Processing is an area of rapid evolution in coffee and where a great deal of innovation and experimentation are taking place. In addition to the washed (wet) and natural (sun-dried-in the whole-fruit) methods, as well as the wet-hulling (semi-dry) processes common in Indonesia and other origins, we now see variations on all these themes, including the honey process (white, yellow, red, and black honey, most embraced in Costa Rica), yeast fermentation methods, and all manner of anaerobic (oxygen-free) processing methods, often applied to the highest-quality coffees (from any origin) to lend them further differentiation and, sometimes, outright uniqueness.

Having such a broad variety of processing choices gives farmers greater control of their coffees at origin, and it ultimately gives roasters control over their product choices and consumer-facing presentation, as well.

Washed process

In most of the world, coffee is typically processed by the washed method, in which coffee cherries have been sorted and pulped to remove the skin, then fermented in tanks of water, where enzymes are created that begin to break down the remaining mucilage on the beans. Fresh water is then used to remove any remaining mucilage. Finally, the green coffee is dried, often on raised (or other) beds in the sun or in mechanical dryers.

Washed processing is best exemplified by Kenya’s classic method, which involves impeccable attention to detail at each stage of the process and tends to result in a “clean,” bright, juicy, balanced cup. The washed process is also commonly used in the origins across Central and South America.

Challenges: it’s difficult to use the washed method for processing coffee cherries if water is scarce or clean water is unavailable.

Natural process

Even though most of the world’s coffee is processed using the washed method, natural processing techniques are even older (more traditional) and are experiencing a sustained revival, especially in the rarified air of the most special microlots. But it’s the traditional method of origins that don’t have access to much water, including Yemen, which produces some of the best coffee in the world.

Simply put, the ripe coffee cherries are picked and sorted, then laid out to dry naturally in the sun, either on concrete patios or raised mats. Daily monitoring is essential to achieve optimal moisture levels, as well as to avoid mold. Management techniques include raking and hand-turning. When the coffee has reached its intended level of drying, the fruit and mucilage are removed, leaving the coffee seed, or bean. The cup produced by this method tends to be more fruit-forward with a fuller body than coffees processed by the washed method.

This method of processing coffee is much less expensive than the washed method, but it is also much riskier because of the possibility of over-fermentation. The natural, or “sun-dried” method, is increasingly popular in the upper echelons of specialty coffee. The goal with these coffees can be to push fermentation to the point of bringing out alcohol notes. In traditional coffee circles, this would not be considered a “clean cup,” but the sensory properties have become increasingly desirable as a means of product differentiation.

Challenges: the natural processing method works best in dry climates; humidity can cause over-fermentation, resulting in undesired qualities such as vegetal notes.

Pulped natural process

Also sometimes referred to as “semi-washed” or “honey” process, pulped naturals are most prevalent in the smallholder farms of Indonesia but can be found in other origins, as well. In this process, the coffee cherries are pulped but some mucilage is left on the bean. Instead of going into a fermentation tank, the coffee goes straight to a drying bed to achieve the optimal moisture level.

Pulped natural coffees can range from sensory profiles akin to full naturals or be more austere and similar to washed-process coffees.

Challenges: mold can be a problem in humid weather conditions and must be monitored carefully during the drying process.

Honey processes

While pulped natural coffees are often referred to as “honey-processed,” Costa Rica has taken the reins on this processing method by introducing many levels of honey-style coffees, including white honey, yellow honey, red honey, black honey, each referring to the relative amount of mucilage left on the beans (with yellow being the least and black being the most). Costa Rican farmers have successfully differentiated their green coffees around the nuances of these differences. Management techniques are subtly different for each level of honey process, with varying intervals for raking and turning, to bring out specific positive attributes in the cup.

Challenges: as with natural-processed coffees, honey coffees must be carefully monitored to avoid off-flavors.

Experimental processes

There are innumerable experimental coffee processing methods, many of which are proprietary or simply tightly held secrets. But some common methods include yeast processing, which involves the addition of wine (or other) yeasts to the fermentation process; anaerobic processing, which involves hermetically sealing the fermentation vessel off from any oxygen source; and post-processing conditioning, such as aging processed green coffee in wine or Bourbon barrels to change the cup profile.

There are seemingly infinite variations on these themes, all designed to differentiate one green coffee from another — and, hopefully, to provide enough excitement in the cup to ask a higher price for the green coffee.