How flavor of coffee is affected by processing

Posted on: 2016-04-12 1:49 PM

As much as the best baristas in America can control a cup of coffee when the kettles are steaming and the scales are beeping, the fate of a bean is sealed far earlier, while still in its green state some thousands of miles aways.
 
A number of factors result in a bean's suggested notes of caramel, stone fruit, pine nut, and sesame. Coffee flavor profiles have to do with genetic cultivars—Bourbon, Caturra, Castillo, and Gesha all carry distinct tastes. Elevation, also plays a role. Lower levels of oxygen in the air create a dense, more complex bean. But to tap into those flavors, coffee must first be transformed from its original state, as the seed of a fruit, into a roast-ready green bean. And how producers handle this transition has a lasting effect on the coffee.
 
The most common ways a farmer treats coffee cherries (the name of the plant's fruit) are called Natural Process, Washed or Wet Processed, and Honey Processed or Pulped Natural. Practices vary by country and region, and myriad permutations can take place on the journey from cherry to bean. Below, the three most popular ways green coffee beans are handled, and how those processes impact your cup.
 
Natural Process
 
Common Flavor Profiles: Diverse, bold, fruity flavors inherited from coffee cherry pulp and skin. Generally produces a heavier-bodied cup.
Regions: Ethiopia, Brazil
 
While the next two coffee processing methods mentioned below require water to treat the cherry, Natural Process, also known as Dry Process or Dry Natural, does not. Hence its name. How it all works is, once a coffee cherry is picked at optimal ripeness, it must dry to a certain moisture content.
 
The cherry sports a skin that wraps snugly around a thin layer of pulp, known as mucilage, all of which encase the coffee beans destined for roast. Usually there are two beans in one seed, coupled together, each covered by a thin layer that called parchment.
 
During the natural drying process, the entire cherry is left intact. The soon-to-be coffee beans still nestled in the center absorb some of the characteristics of that sweet pulp and flavorful cherry skin, until the milling stage when the dried fruit and parchment layer surrounding the bean are hulled.
 
The best natural processed coffees are dried on raised beds common to Africa, a quality practice that, over the past decade, has been disseminated across the globe. Processing the natural way can be riskier than other methods because if the beans are not dried carefully and evenly, the coffee can produce strong off-flavors known as "ferment."
 
Haphazard processing can lead to "dirty" natural, meaning there is a chalky, lingering taste on the tongue. This is why many exporting organizations who source from multiple smallholder farmers promote the washed process (below) instead, where a producer removes the cherry immediately after harvest. In fact, the cherry pulp discarded after the washed process emits a rotting fruit odor as it decomposes, and that’s precisely what coffee pros try to avoid with naturals.
 
Andrea Allen of Onyx Coffee in Arkansas explains that, traditionally, for coffee origins where the washed or wet process is available, dry natural has inherited something of a stigma. In the past, farmers in many regions applied this process to the leftover coffee not suitable for export, so as not to waste time and resources on the added steps. Regardless, it's the oldest way of processing coffee, and the predominant method in some of the most well-known regions, Brazil and Ethiopia in particular.
 
Allen says that only recently has the specialty coffee world begun to recognize the high quality potential of the natural process, which she describes as incredibly diverse, offering a fuller-bodied brew, with notes of "citrus, lime acidity," or a strong "sweet, strawberry jam." Some finer notes can include tropical fruit, bergamot, black tea, and dry chocolate. Nonetheless, Allen regards naturals as a great point of entry for those who have yet to refine their palate: "You don’t have to be a specialty coffee taster to detect the flavors that are evident in naturals because the flavor tends to be really strong and apparent."
 
Washed Process
 
Common Flavor Profiles: "Clean," meaning more flavors inherent in the seed. Well-balanced, complex, pronounced acidity. Silky, delicate, tea-like body, featuring a wide range of notes from starfruit tartness to deep, dark chocolate. More commonly floral.
Regions: Latin America, Africa
 
Nathan Nerswick of Atlanta’s Chattahoochee Coffee has a personal affinity for the subtlety found in Washed coffees, also know as Wet Process. Washed coffees most distinguish themselves from naturals after harvest. Where naturals leave the cherry intact, the washed process separates the bean from the cherry in a procedure called de-pulping. Coffee beans are placed into fermentation tanks, also known as wet mills, and the beans are de-pulped as they pass through a series of stations. First, directly after harvest, coffee cherries are dropped in a hopper at the top of a mill, and water carries the cherries to a holding tank. Any damaged, less dense floating cherries are skimmed off. The good cherries sink and are sent through a de-pulping device. From there the seeds are directed to a fermentation tank to rest for 36-72 hours.
 
Sam Lewontin, co-owner of New York's Everyman Espresso, says that washed coffees are referred to as "cleaner" in taste, though that's not to say they're inherently better. "That sounds like it is pejorative towards natural coffees; it’s not really," he explains. "What we mean is those flavors intrinsic to the seed are communicated more clearly. You don’t have as much flavor of the fruit, more of the seed itself."
 
For this reason, Lewontin says washed coffees often boast "a more pronounced acidity," and this acidity can be enhanced by the small amount of acetic acid that develops organically when sugars in coffee pulp naturally interact with their environment in fermentation tanks. However, if the pH levels are not kept in check during the fermentation process, the acid can proliferate and cause for a vinegary coffee.
 
Nerswick says the balance and complexity of delicate-bodied washed coffee is what fetches more value on a consistent basis. "That’s what the coffee industry has deemed as the pinnacle; Gesha [a variety revered for its delicate, floral quality] often goes for $100 per pound because it has that floral tea-like quality," he says. "I often feel like you’re going to have a more delicate body from a washed."
 
Honey Process or Pulped Natural Process
 
Common Flavor Profiles: Approachable sweetness, jammy, sugary notes. Creamier body than Washed, texture closer to Honey. Not as acidic as Washed, or as high quality as Natural.
Regions: Brazil, Central America
 
For those somewhere in-between the two camps—maybe someone not so excited about the lemon tartness of a washed coffee or the robust blueberry acidity of a good natural—Honey Process or Pulped Natural is the answer. Using the honey process, a producer de-pulps the cherry right after harvest similar to the washed process, however like the natural process, honey process skips the fermentation tanks and leaves any clinging mucilage to dry with the seed.
 
In Costa Rica, depending the amount of mucilage left on the seed, honey process coffee is classified by color, from black to yellow—the lighter the hue, the less pulp left clinging to the coffee seed.
 
"What you wind up with are coffees that have a lot of the sweetness you would expect from a natural process, without a lot of the distinct fruit flavors because you got rid of the skin where a lot of fruit flavor sits," explains Lewontin. Talya Strader of Bay Area roaster Equator Coffees & Teas adds, "Typically you’re going to get a creamier body, muted acidity, and a lot of times it does taste like honey."
 
Strader doesn’t see many honeys reaching extremes on the flavor spectrum: "You might get a strawberry or raspberry, but it won’t be all the way to blueberry. And on the other side, you can still get orange citrus, but none of that super tart lemon. So the mucilage might mute some of those more extreme flavors bringing them closer to the middle."
 
Whether you prefer the syrupy sweetness of a pulped natural, the crisp, tartness of a delicate washed process coffee, or the robust flavors of a natural processed bean, remember that coffee is subjective, and what processing can impart to a coffee is still very much a fluid thing. Within those general methods are innumerable variations that enrich profiles even further. Coffee bean treatment is still a subject ripe for exploration within the industry, and in many cases it’s a process that takes place out of sight and mind, the results of which only the nose and tongue can perceive.