Coffee: The Plant, The Bean, The Process

The Plant

Coffee plants belong to the genus Coffea. There are about twenty-five species of coffee plants. Of these 25 species of coffee plants only two are commonly used commercially, Coffea Arabica and Coffea Robusta. Coffea Arabica growing characteristics and form is more like that of a tree, while Coffea Robusta takes on more of a bush form. As previously mentioned Arabica coffees are more highly prized for their drinkability over coffees for the Robusta variety (see Growing Regions). Sexually, the Arabica plant is self pollinating (autogamous) whereas the Robusta plant can not self pollinate. Once pollinated, dense clusters of fragrant white flowers bloom where the leaves meet the stems. Eventually, small clusters of green cherries begin to form and mature. Once they become red in color they are mature. Most growers hand pick each cherry, an arduous process. Some growers allow the cherries of mature and fall to the ground where they are harvested. The average tree yields only about one pound of coffee per year.

The Bean

So what is all this talk about “cherries”? Each cherry contains two coffee beans contained within a silver skin, a parchment skin, a pulp layer, and a tough outer skin. The inner pulp layer is soft, and has a high sugar content and can be fermented to make coffee liquor or a type of “tea”. In the case of peaberry coffee, only one bean is contained within the cherry.

The Process

How do we get from cherry to a green bean that is ready for roasting? Two methods are generally used to ready coffee for market, a wet process and a dry process. In wet processing the cherry is soaked in water and the skin is removed by pulping. This separates the paired beans, and leaves them covered with a mucilage. The beans are subjected to a fermenting process for about sixteen hours to remove the mucilage. The beans are dull green in color at this point where they are discharged onto a large drying patio where the moisture content of the bean is reduced to about 12%. The beans are then hulled, graded, and ready for market. Some growers, particularly Brazilian growers of Robusta coffees, use a dry process method where whole cherries are spread out and allowed to dry and shrink naturally. The beans are then hulled and graded. What is grading? Grading is generally sizing the beans and quantifying the number of defects in the beans. Unfortunately, there is no worldwide uniform standard for bean grading and it varies from country-to-country, and government-to-government. Some of the indicators for the largest beans: A in India; AA in Kenya, Tanzania, and New Guinea; AAA in Peru. Columbian premier coffee is labeled Supremo, while a blend of Supremo and lesser-graded beans are labeled Excelso. Grading is important at the time of roasting. Small beans roast faster than large beans and evenly sized / graded beans result in a more uniform roast. Coffee is generally packed and shipped in 60 kilogram (130 pound) burlap sacks with the silver skin intact. This skin is removed when the bean expands and collected as “chaff” during the roasting process.