There are many factors that make different coffees taste the way they do, and one of the factors you most often see on coffee bags is the way that particular coffee has been processed. While processing is by no means simple, it is one of the factors we actually understand the impact of fairly well. So let’s break down exactly how it works, and what kind of flavors you can expect based on the processing method you’re buying.
To get back to basics: coffee is a fruit. And you can’t really understand how processing works without understanding the structure of that fruit. The outside layer of the fruit is, rather predictably, called the skin. Inside the skin , again just like most fruit, we get a layer of pulp. Inside that pulp, there’s a protective layer that, because of its texture after it dries, we call the parchment. Inside that, there’s a very thin layer called the silverskin. And, finally, that silverskin clings to a seed , which is the actual thing we call a “coffee bean” and end up roasting, grinding, and brewing to make coffee.
In addition to a whole bunch of logistics and travel, there are two main things that need to happen for us to get from that picked coffee cherry to a roastable coffee bean: the coffee must be dried and the layers must be removed down to silverskin. The combination of those two things is basically what we mean when we say “processing,” and different processes are just different orders of operation for that drying and removal.
A disclaimer I like to make before going in-depth on processing or any other flavor factor is that coffee is super-complex and processing is just one of many, many flavor factors. So, for example, if you have a low-elevation coffee of a variety that doesn’t tend to produce any fruit notes, you’re not going to make it taste like blueberry bubblegum by naturally processing it. And if you have a naturally processed coffee with a big body, you can still make the body thin by brewing it with too much water. And so on and so forth. So remember, processing is very, very important, but it’s just one of many pieces in our coffee flavor puzzle. Let’s get into the big four processing methods, how they work, and what flavors you’re most likely to find in them:
One very common processing method is the washed process. In the washed process, the skin and pulp are removed from the cherry before the coffee is dried. This can be accomplished in different ways. Often the coffee is fermented either underwater or in a dry-fermentation vessel of some sort. That fermentation loosens the pulp (and, if it hasn’t already been mechanically removed, the skin), which allows it to then be removed through agitation. This can take a lot of forms, from mechanical methods to workers manually agitating the fermented cherries with paddles. The fermentation that happens in this kind of processing affects flavor, but if done properly it doesn’t usually lead to over-ripe flavors you might associate with the word “fermented”. Washed process can also be done without fermentation, using machines with tiny jets of water that forcefully remove that fruit layer.
After the pulp and skin are gone, washed coffees are dried with just the parchment, silverskin, and seed. The parchment is then removed after drying, leaving just the silverskin-covered seed to be roasted (the silverskin comes off during the roast). Washed coffees tend to have more acidity and less body than other processes. So if you’re drinking a coffee that’s super bright or super gentle, it’s likely washed.
What’s on the seed during drying?: Silverskin and parchment
Flavor factors: Higher potential for acidity, lower body.
Popular examples: Clean, balanced Colombians; citrusy Kenyans; gentle, floral Ethiopians
Natural processing is so called because it mirrors what would happen if the coffee just naturally fell off a tree. The whole fruit — skin, pulp, and all — dries together, and it’s not until after drying that the skin and pulp, along with the parchment, are removed. This leads to lower perceived acidity and heavier body, and in many cases can lead to ultra-ripe, jammy, and candylike fruit flavors. If you’ve ever had an Ethiopian coffee that tastes like blueberries, for example, that’s probably a natural. I don’t feel all the way comfortable, however, saying that natural coffees are fruitier. For example, you’re more likely to find a washed coffee with lemon acidity or gentle peach flavors. And it wouldn’t make sense to say that blueberries are fruitier than lemons, right?
Wild fruit flavors are only one possible outcome of natural processing. Many of the kinds of Brazilian coffees that taste like chocolate and nuts and are the basis for many house and espresso blends are also naturals. Those coffees aren’t going to be fruity no matter how you process them, so the natural process reinforces that big body and dense sweetness.
What’s on the seed during drying?: Silverskin, parchment, pulp, and skin
Flavor factors: Lower potential for acidity, higher body, more ripe/preserved/candied fruit flavors
Popular examples: Blueberry bomb Ethiopian coffees; big-bodied, chocolatey Brazils
Honey processing (aka pulped-natural) is easy to think about as a sort of midway point between washed and natural. The skin and some of the pulp are removed from the seed, but some percentage of pulp is left on the parchment during drying. It’s popularly known as “honey,” because that sticky pulp layer is referred to as “miel,” the Spanish word for honey in Central American coffee-growing countries. This process was invented in Brazil, but became really popular in specialty coffee around a decade ago when farmers in Costa Rica began producing some really wonderful coffees. You might hear terms like “red honey” and “yellow honey”, and those describe different types of honey processing, but are unfortunately very far from standardized. They most often refer to the percentage of pulp left on the bean, but I’ve also heard them refer to completely different things, like how often the coffee is turned on a drying bed.
What’s on the seed during drying?: Silverskin, parchment, and some pulp
Flavor factors: The happy medium between washed and natural
Popular examples: Syrupy, complex Costa Ricans; more gentle-than-usual Brazils
We use the term “hulling” to describe the removal of the parchment layer from the coffee cherry. So another way to phrase the main difference between the processes we’ve learned about so far is: what is on the parchment when it is being hulled? Is it the skin and the pulp (natural), just some pulp (honey), or nothing at all (washed)? What all those processes share is that hulling happens after the coffee is dried, usually to around 12 perecent of its original moisture content. In the wet-hulled process, the skin and most or all of the pulp are removed before drying, but the coffee dries in parchment only to about 50 percent moisture, gets hulled, and then dries the rest of the way with just the silverskin protecting the seed from the elements.
This seemingly minor variable makes a huge difference in flavor — at their best wet-hulled coffees have a pleasant earthiness, at worst they’re muddled or downright dirty tasting. The wet-hulled process is only really performed in the coffee-producing islands of Indonesia, most famously Sumatra and Java, where humidity and rainfall make this faster processing style more necessary. If you like earthy notes in your coffee, it’s a process to look for.
What’s on the seed during drying?: Silverskin, parchment and sometimes pulp for the first part of drying, just silverskin for the rest of it
Flavor factors: Earthy, less clear acidity
Popular examples: Big-bodied, earthy Sumatras and Javas
To complicate things further, there are differences in the drying part of processing itself. Drying can happen mechanically, in big drums that resemble elongated clothes dryers or lower temperature coffee roasters. That style of drying was frowned upon in specialty until fairly recently, because we associated machines with drying coffee too quickly and at too high of a temperature. We now know — because of quality-focused farmers and mills — that when done with care it can be more controllable and therefore more consistent than drying out in the sun. Drying in the sun has many variations as well, with everything from concrete drying patios to raised beds that let air circulate underneath the coffee, “solar dryers”, which are raised beds that use greenhouse-like plastic roofs, and even just tarps laid out on the side of the road.
Drying is incredibly important, but if you’re just trying to categorize a coffee into one of our main processing methods, I’d actually advise not getting too hung up on it. Some roasters have started to refer to their natural coffees as sun-dried naturals, which is accurate, but can also be confusing, considering their washed coffees are mostly sun-dried as well.
There are a thousand variations on how to wash a coffee, with more being invented and experimented with as we speak. People are trying to control the specific types of yeast used in fermentation for different results instead of just letting whatever yeasts are present in the air do their thing. Others are introducing acids such as lactic acid in fermentation to effect different flavor results. Some farmers are experimenting simply by using processing methods not usually used in their growing region. This involves a lot of new infrastructure and risk, so producers can’t simply change methods on a whim, but we’re seeing things like natural coffees from Burundi and honey process coffees from Sumatra, combinations that just didn’t exist a few years ago. We’re even seeing roasters get their hands on coffees of two or three different processes from the same exact place, giving you opportunities to really taste the difference in processing when all the other factors are equal.
For most producers, experimentation isn’t an affordable luxury (just growing coffee itself is financially risky enough), and improvements are more incremental. The general processing type might remain the same for decades, but seemingly minor improvements in equipment and techniques improve consistency and flavor in very noticeable ways. So even if you don’t see a flashy or unusual processing method on a bag, know that all the work that has gone into separating that seed from the rest of that cherry has had a huge impact on your coffee's taste.
That’s a lot of rules and caveats, but all in all it’s pretty simple. Like clean flavors and juicy acidity? Take a look at some washed coffees. Big bodies and wild flavors? Go natural. Earthy notes more your thing? A wet-hulled coffee will get it done. And the fact that there are coffees out there that break all those rules just makes things more interesting.