We Need Simple Categories
Many specialty products are organized into categories that make them more approachable. In the world of wine, knowing the answer to the question, "red or white," can help a customer feel empowered and confident enough to explore further 'subcategories' within their purchasing decision.
Historically in coffee, this categorical empowerment has been associated more with roast style than the actual qualities of the bean. Now that we are becoming more aware of details that determine bean character (and putting roast style aside), what should be our basic categorization for specialty coffee?
Assuming all other details are the same, there is no question that processing (how coffee cherry fruit is removed) is the easiest difference to taste. This is a convenient category since there are two major traditions that have developed, allowing for a beautiful contrast. Coffees that use a method of fruit fermentation and running water are known as 'washed' coffees. When no water is used and the cherry fruit is left to 'raisin' before being milled off, this is known as 'natural' processing.
The differences between these two are so intense in the cup that some will actually go as far as to call their preferred processing method the only 'real' option. It is similar to asking an Irishman and a Scotsman the proper way to make whiskey (or whisky, respectively).
For Love of Acidity
Washed coffees are known for being balanced, clean, and sweet with nuanced acidity. Since no fruit is dried on the bean, there are fewer chemical changes that happen, making washed coffees less of a 'fruit' product and more of a 'seed' product. Washing requires an abundance of water, which is why it developed first in growing regions which have this resource. Water conservation techniques in recent years have led to more widespread washing stations worldwide, but many growing regions still favor natural processing.
It is virtually impossible to talk about the flavor of a good washed coffee without discussing the quality of its 'acidity'. A connoisseur of washed coffee will often celebrate acidity in the same way a fan of the India Pale Ale style of beer will celebrate 'hoppiness.'
In contrast, naturally processed coffees will capture adjunct flavors from the drying fruit of the cherry. These flavors generally contribute a berry-like quality or a wine-like complexity. Naturals are typically not described as being 'clean', but can often be balanced and sweet in spite of their relative intensity. Natural coffees also have 'acidity' but it is usually not the defining characteristic it is for a washed coffee. Those who have developed a palate for naturally processed coffees will crave the wild and saturated flavors they offer.
The Processing Spectrum
Washing and naturally processing are two ends of a spectrum; there are many variations and hybrids to learn about as well. Pulped natural, semi-washed, super-washed, honey process, and wet-hulled are among these other methods. Many of these are the result of experiments to find a sort of 'middle way' for one reason or another.
Try not to get too caught up in the nuances of all of these variations at first. A lot of it can be over-hyped and over-stated (surprise, surprise) and the most important thing is to become familiar with the contrast of the two extremes.
If you don't already know which you prefer, ask your local roastery if they have options from the different traditions for you to taste side-by-side. Chances are, you will amaze yourself with how clearly you can taste the contrast. This ability to differentiate is extremely empowering and will be your gateway for years of further exploration.