You don’t have to visit too many coffee shops or look at that many bags of coffee to realize that coffee roasters like to tell you a lot of information about the coffee, from where it was grown, which variety the plant is and altitude to the type of processing the coffee went through before it got roasted.
This is actually pretty important information. I explored altitude a little but in a previous post which will be expanded on in the future, but this seemed like a good opportunity to start an education series on coffee, so here’s the first official article on “wet processing” or “washed” coffee.
Processing is what happens to coffee between the time the cherry gets picked from the shrub until it is shipped in its relatively stable “green” form prior to roasting. Processing has a big impact on the flavor of the coffee and so, as a consumer, it’s helpful to know what roasters mean when they put things like “washed” or “natural” or “honey processed” on a label because it will give you some expectations for what to expect in the cup. And, heck, you might just be interested to know how your coffee got to be in that bag in the first place!
When discussing coffee processing it helps to know a little bit about the anatomy of the coffee cherry, the fruit of the coffee shrub. The coffee “beans” we know and love are actually the seeds of the coffee cherry and most cherries contain two, although some only contain one, called a “peaberry.”
These seeds have a membrane around them called “silver skin” (when roasting coffee, this stuff jumps off and makes a mess and in that case gets a name change to “chaff.” Around the silver skin is a thicker membrane called parchment, and then there is pectin and pulp (together making up what is usually referred to as “mucilage”) inside the cherry, too. The point of processing is to remove the pulp and sometimes the parchment from the seeds and this can be done a whole lot of ways.
Wet processing produces a “washed” coffee by using water, friction and a little fermentation to remove the pulp and mucilage from the seeds inside. Once coffee has been picked and sorted, weighed and whatever else they do before it gets to processing, the cherries are added to a pulping machine that slices them open and squeezes the beans out, separating them from most of the cherry.
What’s left behind is the coffee beans/seeds with a goopy layer of mucilage still clinging to the parchment, and this stuff needs to be separated or else things will start to rot, mold and get funky pretty quickly. In other processing methods, the mucilage isn’t removed and will contribute to further flavors down the road in the process, so washed coffees are what they are when the mucilage is removed and do not benefit from these sugars and nutrients once they are removed, of course.
To get rid of the mucilage, processors move the slimy mucilage-y beans to fermentation tanks where bacteria ferment the sugars in the mucilage. This can take from a handful of hours to a few days, depending on lots of factors, but the end result is that the mucilage gets removed, leaving the coffee beans and their parchment covering behind.
Some processors also use a mechanical demucilaging machine to remove some of the mucilage prior to fermentation and it is thought that, like fermentation, they can calibrate this process to achieve different results in the flavor profile of the beans based on how much mucilage is removed and how long it sticks around before fermentation. There’s a lot to this whole processing thing!
After all this separating has occurred, the parchment needs to dry quickly or, again, rotting can happen or off-flavors can easily develop that stick with the coffee, so the next step in processing would be drying. Drying coffee is a process in and of itself and will also be a future article in its own right.
As a rule of thumb, washed coffees tend to be clean, bright and relatively mild compared to other types of processing, but as you can imagine there are as many approaches to wet processing coffee as there are people doing it!