Edited February 9, 2015
I recently helped with a Q Grader course here in Singapore (the first ever in-country) and after the course a few of us went out for drinks and dinner to celebrate and a pretty good debate over inherent quality ensued.
The topic of the debate was whether coffee's inherent quality could be improved post-processing of the green beans. I contended it couldn't in any meaningful fashion and the others (roasters by trade) argued that they could indeed improve a coffee's quality in the roast.
The basis of my argument follows:
Coffee's inherent quality is “baked in” at origin through several factors, including environmental conditions, genetic make-up of the coffee trees, agronomy practices, farm operational management and finally, cherry processing post-harvest. It is in these domains that the ingredients for quality are baked into the coffee bean. All subsequent processing of the bean after cherry processing is manipulation of the existing bean ingredients — its constituent parts — the organic acids, sugars, fats, carbohydrates, water, etc. These original ingredients of the bean determine all subsequent ingredients (chemical compounds) that are formed or destroyed in all subsequent phases such as transport to storage, resting in storage, possible export and further storage, roasting, possible further transport, and finally brewing.
Can one make a bad coffee a little better, more desirable, through advanced roasting, brewing, and marketing techniques? Yes. A borderline-bad coffee can be made more desirable as a consumer product, but you can not change the coffee's inherent quality.
Environmental conditions affecting coffee quality
Coffee begins as a tree best cultivated in a very specific climate; between 25°N and 25°S latitudes; —the tropics — and at elevations of between roughly 1,000 and 2,000 meters above sea level — the mountains. It prefers less-ancient soils, meaning typically volcanic soils. It produces the best fruit at the highest elevations, where temperatures cool significantly overnight allowing for a slower development of a more complex cherry. Inside the cherry are (usually) two seeds, which eventually become coffee beans. These seeds are living, organic material that is fed and nourished by the tree, which draws nutrients from its environment in a manner dictated by the operational management of the farm.
Genetic make-up of the coffee trees
There are different species of coffee trees, such as coffea arabica and coffea robusta, each containing different subspecies; varieties and cultivars. Starting at the top of the taxonomy tree, the different species represent very different levels of quality. C. arabica trees produce seeds with twice as much sugar and half as much bitter caffeine as c. robusta, generally making the taste of arabica coffee superior to robusta. The same is true as we move down the taxonomy tree into varieties and cultivars: there are varying levels of quality between different varieties and cultivars. Therefore the farmer's choice of which trees to plant is one of the earliest and most influential factors determining the quality of a given coffee.
Farm operational management
The farmer determines the inputs (fertilizers, sometimes irrigation, sometimes pesticides) to use, when to use them and how much to use. The farmer prunes the trees to define its shape, which determines where it focuses energy towards growth with the goal of focusing a majority of its energy on fruit development rather than new wood development.
The distance between each planted tree and any crop planted along side the coffee (a technique called intercropping) can also have an affect on quality. For example, banana trees planted too close to coffee trees will compete for valuable soil nutrients. When a coffee tree faces a crisis of resources, it will preserve the trunk over the the cherries, thus cherries will lack in complex sugars, carbs, etc so that the trunk may survive.
Cherry processing, post-harvest
Once the cherry has matured to a beautifully red ripeness, it is harvested and processed to remove and dry the seeds to a specific level of moisture; between 11 - 12%. The processing method can vary but regardless of the method used, it has a significant impact on quality. Poorly processed coffee can contain many defects such as mold, overly fermented beans, physically damaged beans, seeds from under- or over-ripe cherries, etc.
Post-harvest processing is the last phase that stabilizes the seed (or bean) and makes it a raw product that roasters use to make roasted coffee beans.
All of the factors above combine to form the terroir1:
The terroir is a system of complex interactions between a set of actions and techniques conducted by men, an agricultural product, and a physical environment to be developed through a product, to which it confers a particular originality. The terroir is therefore a geographical area combining a physical environment, know-how, practices that are often applied in response to the environment and derived from a local history, and a product with original characteristics.
And it is the terroir that determines the constituent parts of a coffee seed (bean) that ultimately determine the inherent quality of a coffee. These constituent parts are later manipulated by roasting and brewing. I'm not saying that the roaster and the brewer have no impact on quality. They certainly do. But they can only work with the ingredients that are "baked in" at the farm and processing mill.
Updated February 9, 2015: stylistic changes
1. Coffee: Terroirs and Qualities, QUAE, 2007, p. 52↩