Understanding coffee flavor the Bean cleaning and processing methods

Coffee and coffee flavor are like two best friends with unclear boundaries. They go together, they need each other, and yet they are still distinct. Coffee, in the broadest sense, has a very identifiable taste but each coffee’s flavor profile is nuanced and developed at each stage of the bean’s existence, starting with coffee plant species and ending with brew method. Today, we’re going to deconstruct the coffee flavor profile paradigm and in doing so, (hopefully) equip you with the knowledge needed to identify coffees that strongly exhibit the characteristics you value most in your cup. First up? Bean type and terroir.

Bean structure: plant species and terroir

Bean species, variety, and growing terroir collectively create a bean’s structure, which includes basic flavor and textural characteristics. While there are over 100 coffee species, the two primary species are Arabica and Robusta. Arabica plants are high-grown, shade-grown (i.e., they are grown under large shade trees with no direct sun exposure), and require six months+ to bring their seeds to maturation. This prolonged, arduous growing period offers the seeds ample time to develop complex, nuanced sugars and acidity. Arabica seeds tend to be smooth, pleasantly flavorful, and pleasantly aromatic. Robusta plants, on the other hand, are low-grown, sun-grown (i.e., fast grown), and produce multiple crops per year. Robusta seeds are caffeine-packed and produce a bitter, almost burnt smelling coffee. Within the Arabica and Rubusta species exists numerous bean varieties, or organic mutations. These varieties maintain the species’ intrinsic attributes (i.e., flavor notes, texture, etc.) but vary in one or more significant way from the source variety. Varietals often develop as a response to new environmental factors — or terroir. Terroir is the everything of a particular piece of growing land or region — the soil composition, rainfall, altitude, temperature, humidity, and sunlight— and it determines the coffee’s tones and texture. Elevation, for example, impacts a bean’s sweetness and acidity while soil composition controls water availability and nutrient content. Collectively, species, variety, and terroir create the bean’s structural characteristics (flavor, acidity, texture, and aromatics).

To learn more about bean species, bean variety, or terroir, please scroll to the links at the bottom of this entry.

Bean cleaning: processing method

Coffee beans are the seeds of coffee cherries. Before being roasted, these seeds must be cleaned or processed, the physical act of separating the coffee pulp, mucilage (a sticky sweet, honey-flavored substance separating the parchment from the pulp), and parchment (or hull) from the green seeds. There are four primary processing methods, dry, wet, semi-washed, and honey processed. The processing method used on a bean impacts its acidity, flavor, and texture. Dry processed beans ferment with their cherry pulp still attached and absorb its sweetness. Wet processed beans are cleaned prior to fermentation and, while very pure in seed character, are generally less acidic than dry processed beans. Semi-washed beans have their husk and some of their mucilage removed prior to fermentation. Unlike wet processed beans, which ferment in water tanks, semi-washed beans are dried on a solid surface such as brick or earth and absorb flavors from their drying surface. Finally, honey-processed beans are dried with a specific percent of their mucilage still attached to increase the bean’s natural sweetness. The amount of mucilage remaining during fermentation determines the color and honey-sweetness of the bean. While processing does not change the structure of the bean, it does influence flavor and how structural characteristics present in the cup. The chemical / structural change happens during roasting.

Bean chemistry: roasting and the Maillard Reaction

Green coffee seeds are a raw, and like any other seed, their chemical composition alters when heated. The longer the bean is exposed to heat, the greater the structural change. For coffee, this primarily means a structural change in the bean’s sugars (which break down into a simple sugar group, carbonyl group, and a group of amino acids called the nucleophilic amino group), proteins, lipids (fats), and minerals. In more scientific terms, the coffee bean undergoes a Maillard Reaction when heated between 284 to 329° Fahrenheit (140 to 165° Celsius). During the Maillard Reaction, the bean’s sugars split into two groups, the amino acids group, and the simple sugar group. The simple sugar group breaks down, turns brown, and releases flavor and aromatic notes when undergoing the Maillard Reaction. The longer the bean roasts, the greater the breakdown. Eventually, these sugars and acids liquify and create an oil sheen on the bean. At this stage, the coffee bean is now roasted, and the art of muting, accentuating, and essentially choosing which of the bean’s 1,000 aromatic and 850 flavor notes are present in the final roasted bean, as well as the coffee’s final texture, falls to the roaster.

A coffee roaster is like a chef, working with the raw materials of whichever coffee or coffees (s)he is using and roasting them to the point where their best characteristics dominate. Lighter roasted coffees are brighter, lighter in both mouthfeel / texture and shade, and tend to have delicate sweet fruit, floral, citrus, and berry notes. Medium roasted coffees often highlight a bean’s textural characteristics and dominant notes, meaning that some of the light, bight upper notes may be lost. Dark roasts are roasted to a shade profile and tend to have heavier mouthfeel (the more oil on the bean, the heavier the texture) and pronounced nut, earthy, and / or chocolate notes.