COFFEE PROCESSING

Take a tour with Coffee Research and How Stuff Works at how coffee beans are processed.

Coffee trees produce berries, called coffee cherries, that turn bright red when they are ripe and ready to pick. The fruit is found in clusters along the branches of the tree. The skin of a coffee cherry (the exocarp) is thick and bitter. However, the fruit beneath it (the mesocarp) is intensely sweet and has the texture of a grape. Next comes the parenchyma, a slimy, honey-like layer, which helps protect the beans. The beans themselves are covered by a parchment-like envelope called the endocarp. This protects the two, bluish-green coffee beans, which are covered by yet another membrane, called the spermoderm or silver skin.

There is usually one coffee harvest per year. The time varies according to geographic zone, but generally, north of the Equator, harvest takes place between September and March, and south of the equator between April and May. Coffee is generally harvested by hand, either by stripping all of the cherries off the branch at one time or by selective picking. The latter is more expensive and is only used for arabica beans.

Coffee pickers can pick between 100 and 200 pounds (45 and 90 kg) of coffee cherries per day. Only 20 percent of this weight is the actual bean.

There are three processes that are commonly practiced including the wet-process, the dry process and the semi-washed method.

The coffee cherries are brought to the processing plant immediately after harvesting.

Ripe, overripe, and under-ripe cherries are mixed together at this point. If they were not separated the coffee would have a dusty unpalatable flavor with few desirable attributes.

The beans are first washed with water and then passed into tanks filled with water for preliminary separation. The best coffees are dense and will sink in water, whereas the overripe cherries will float and are separated. The low-quality coffees are either slated for internal consumption or sold to instant coffee producers in the United States or Europe.

Unfortunately, green (underripe) cherries are also dense and will continue to be mixed with the perfectly ripe cherries. The green cherries can be sorted out during wet-processing, or in the case of dry-processed coffees must be sorted at a later time.

In the wet-process, the ripe cherries are pulped (removed) from the cherry by applying pressure. With the right pressure only the ripe cherries will be pulped, whereas the hard unripe cherries will be separated. The beans are then sent to fermentation tanks where they remain in water for approximately 8-20 hours.

During this time, the mucilage ferments and is washed from the bean. Wet-processed coffees are characterized by their bright and clean tastes. The body and sweetness, however, is diminished relative to dry-processed coffees.

After the mucilage is removed in the fermentation tanks, the coffee is dried on patios, in mechanical dryers, or using a combination of the two. Almost all coffee producing regions will have slight variations in drying practices. The goal is to prevent fermentation, which is a undesirable fruity spongy flavor resulting from molds in the coffee.

Instead of the wet-process, the weather in certain regions allows producers to use the dry-process (natural process). After the "floaters" are removed from the "sinkers" in the initial separation, the coffees are simply dried on large patios or in mechanical dryers. The drying time is longer and fermentation is more frequent. However, since the coffee remains in contact with the sweet mucilage longer, the coffee has a sweeter taste and heavier body. On the other hand acidity, cleanness, and flavor are often diminished. Natural processed coffees are almost always used in espresso.


The third process called semi-washed (pulped natural) is relatively new and is fairly limited. Only countries that have a distinct and long dry period can process their coffees using the semi-washed method. In this process the coffees are pulped, but the mucilage is not removed by fermenting in tanks. Instead, it is allowed to dry with the coffee. Therefore, the semi-washed method results in a coffee that shares the characteristics of both the wet- and dry-processes. The coffee has a nice acidity, sweetness, flavor, and aroma, but none of these aspects are as potent as the strictly dry- or wet-processed coffees

After the coffee is dried, it is stored for a short period of time in pergamino and the pergamino is removed prior to shipping in a process called hulling. Keeping the pergamino intact during storage helps preserve the flavor and aroma of the coffee. The coffee is then packed into 60 kg burlap bag sacks and exported.


The importer will then send the coffee to coffee roasters around the country.