Coffee Bean Varieties and Coffee Processing

The Coffee Bean

The quality of your cup of coffee starts with the type of coffee plant, how it’s grown, where it’s grown and how the coffee fruit, or cherry is handled and processed all the way to the green coffee bean. The two most commonly grown coffee beans are Robusta (Coffea canephora) and Arabica (Coffea Arabica). Coffee beans are cultivated in Latin America, Southeast Asia, and Africa. Once ripe, coffee berries are picked, processed, and dried.

Robusta Coffee has its origins in western Africa. It is grown mostly in Africa and Brazil, where it is often called Conillon. It is also grown in Southeast Asia where French colonists introduced it in the late 19th century. In recent years Vietnam, which only produces Robusta, has surpassed Brazil, India, and Indonesia to become the world's single largest exporter. Approximately one third of the coffee produced in the world is Robusta.

Robusta coffee is easier to care for than Arabica coffee, and, because of this, is cheaper to produce. Since Arabica beans are considered superior, Robusta is usually limited to lower grade coffee blends as a filler. It is however included in instant coffee, and in espresso blends to promote the formation of "crema". Robusta coffee has about twice as much caffeine as Arabica coffee.

Arabica Coffee is a species of coffee indigenous to Ethiopia and Yemen. It is also known as the "coffee shrub of Arabia" or "mountain coffee". Arabica is believed to be the first species of coffee to be cultivated, being grown in southwest Arabia for well over 1,000 years. Arabica coffee is considered to produce better coffee than Robusta coffee. Gourmet coffees are almost exclusively high-quality mild varieties of Arabica, like Colombian coffee. Arabica contains less caffeine than any other commercially cultivated species of coffee.

Commercial Coffee is almost always a blend of Arabica and Robusta beans and is also a blend of the same bean variety from different growing regions around the world. Blending is done to achieve the roasters flavor profile goals. Even gourmet coffees that are composed of exclusively Arabica beans will be blended to achieve a particular taste profile.

Coffee Processing

Coffee beans are the seeds of fruits which resemble cherries, with a red skin when ripe. Beneath the pulp, surrounded by a parchment-like covering, lie two beans, flat sides together. When the fruit is ripe a thin, slimy layer of mucilage surrounds the parchment. Underneath the parchment the beans are covered in another thinner membrane, the silver skin (the seed coat). Each coffee bean fruit, or cherry generally contains two coffee beans but the fruit can contain one or three coffee beans . Coffee beans must be removed from the fruit and dried before they can be roasted; this can be done in two ways, known as the dry and the wet methods. When the process is complete the unroasted coffee beans are known as green coffee.

The dry method (also called the natural method) is the oldest, simplest and requires little machinery. The method involves drying the whole cherry.

First, the harvested cherries are sorted and cleaned, to separate the unripe, overripe and damaged cherries and to remove dirt, soil, twigs and leaves. Then the coffee cherries are spread out in the sun, either on large concrete or brick patios or on matting raised to waist height on trestles. As the cherries dry, they are raked or turned by hand to ensure even drying. This step may take up to 4 weeks before the cherries are dried to the optimum 12.5% moisture content, depending on the weather conditions. On larger plantations, machine-drying is sometimes used to speed up the process after the coffee has been pre-dried in the sun for a few days.

The drying operation is the most important stage of the process, since it affects the final quality of the green coffee. A coffee cherry that has been over dried will become brittle and produce too many broken beans during hulling. Coffee that has not been dried sufficiently will be too moist and will rot when attacked fungi and bacteria. The dried cherries are stored in bulk in special silos until they are sent to the mill where hulling, sorting, grading and bagging take place. All the outer layers of the dried cherry are removed in one step by the hulling machine.

The dry method is used for about 95% of the Arabica coffee produced in Brazil, most of the coffees produced in Ethiopia, Haiti and Paraguay, as well as for some Arabica coffees produced in India and Ecuador. Almost all Robusta coffee beans are processed by this method.

The wet method requires the use of specific equipment and substantial quantities of water. Coffee beans produced by the wet method are usually regarded as being of better quality and commands higher prices.

Just like the dry method, the harvested cherries are sorted and cleaned, to separate the unripe, overripe and damaged cherries and to remove dirt, soil, twigs and leaves. After sorting and cleaning, the pulp is removed from the cherry. This operation is the key difference between the dry and the wet methods, since in the wet method the pulp of the fruit is separated from the beans before the drying stage. The pulping is done by a machine which squeezes the cherries between fixed and moving surfaces. The flesh and the skin of the fruit are left on one side and the beans, enclosed in their mucilaginous parchment covering, on the other.

The pulped beans go on to vibrating screens which separate them from any unpulped or imperfectly pulped cherries, as well as from any large pieces of pulp that might have passed through with them. Then the separated pulped beans then pass through water-washing channels where a further flotation separation takes place before they are sent to the next stage.

The newly pulped beans are placed in large fermentation tanks in which the mucilage and any remaining pulp is broken down by natural enzymes until it can be washed away. For most coffees, this takes between 24 and 36 hours, depending on the temperature, thickness of the mucilage layer and concentration of the enzymes.

The coffee is thoroughly washed with clean water in tanks or in special washing machines. The wet parchment coffee at this stage consists of approximately 57% moisture. To reduce the moisture to an optimum 12.5% the parchment coffee is dried either in the sun, in a mechanical dryer, or by a combination of the two. The sun-drying is done on extensive flat concrete or brick areas, known as patios, or on tables made of fine-mesh wire netting.

After drying, the wet-processed coffee, or parchment coffee as it is commonly known, is stored and remains in this form until shortly before export.

The wet method is generally used for all the Arabica coffees, with the exception of those produced in Brazil and the Arabica-producing countries mentioned above as users of the dry method. It is rarely used for Robusta coffees.