First an introduction to our friend, the Coffea arabica. Coffee plants were initially observed in the highlands of Ethiopia, Yemen and southern South Sudan. The coffee tree itself grows best at high altitudes and does not tolerate subfreezing temperatures. The flowers of the tree are white, the scent that of Jasmine. In fact this lead
Jussieu, to name it Jasminum arabicum. The great Linnaeus placed it in its own genus later. The ripened fruits of the tree are red and called cherries. The tree takes five years to mature to a point of providing useful yields. The fruit takes 9 months to fully mature/ripen although apparently there is some flex in that as trees in Columbia, South America can flower (thus produce fruit) twice a year. Deep inside under several layers normally there are two coffee beans, called flat beans (one side rounded the other side flat).
Sometimes only one is present, called a peaberry. This is a larger more oval bean. These peaberries are set off and used for a separate type of coffee. Most peaberry is associated with Tanzanian coffee; Kona coffees (grown in Hawaii) also produce a peaberry with some regularity.
When a coffee bean is harvested it is encased in the cherry. Sometimes green cherries are also picked. These greens are not ripe and will tend to produce a poor end product. This is what your mass producers use as they are cheaper. Cherries can be picked by hand or mechanical. In some parts of the world theft of crop is an issue which may encourage an early mass picking. There are two main methods to processing the bean of Coffea arabica wet and dry processing.
The primary methods of wet processing are ferment and wash and machine washable. Ferment and wash allows the fruit to break down over the bean and is then washed off. This has to be monitored closely to prevent absorption of undesired flavors. This stage takes from 24 to 36 hours. Machine washing uses a mechanical process to separate the fruit from the seed. With the machine wash process the chance for the pulp of the fruit to influence flavor is lost. Then the bean must be dried out, this is done by sun or machine. There is quite a bit of moisture in the shell surrounding the bean. This has to be dried out. The final result of this is a relatively dry bean (10% of its original moisture content) which needs to be hulled. Drying out will result in what is called a parchment bean. There will be a covering over the bean that is dry like parchment and can be crumbled off easily. The parchment will have a sand paper texture.
Dry processing is fairly straight forward.
Old fashioned layout in the sun drying or in a solar dryer or mechanical. With sun drying the fruited beans are laid out in the sun and simply dried. This can take up to four weeks. Dry processing results in a pod. This is the dried cherry wrapped around the bean. The pods will be dark in color. Sometimes machines are employed to speed the process up or take over if humidity or rain is preventing the drying process from reaching success. Smaller scale operations can use a “solar box” to capture and utilize sun without direct contact. This process allows for the cherry to impart more flavor on the bean.
After the beans have reduced to the proper moisture levels (which must be monitored closely to avoid mildew) they can then be hulled. From the processing process thus far a skin will be left over the beans. Sometimes it the beans will be polished to improve appearance and remove the silver skin and chaff.
After all that the beans are not yet done. Now they must be sorted according to size, density and color. There are machines that will do this much more quickly than people ever could for density. For color the best tool is the human eye. This can be done by machines by passing the beans through a camera focus that tests for color and uses compressed air puffs to separate the off color (and therefore undesirable) beans. How these machines do this fast enough is mind boggling.
* Sweet Maria’s Coffee in Oakland California has awesome videos on youtube. Some of them are shot on a flip cam so they are not the highest resolution but the content is incredible.