Robusta Coffee Beans
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. 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.