thumb|Traditional coffee drying in [[Boquete, Panamá]]
Coffee production is the industrial process of converting the raw fruit (the coffee cherry) of the coffee plant into finished coffee beans. About eight months after coffee cherries appear on a coffee plant, the cherries are harvested either by hand or by machine. Then they are, depending on the method, pulped and then dried or simply set out to dry. After this, the beans are stripped of their remaining dry skin and fruit residue. Once they are cleaned, sorted, and graded, they are suitable for distribution. While all green coffee, produced from immature coffee beans, is processed, the method that is used to process coffee varies, and significantly affects the flavor of coffee once it is roasted and brewed. Coffee production is a major source of income for 12.5 million households, most in developing countries.
Picking
thumb|Coffee bean harvesting machine, [[Mareeba, Queensland, Australia]]
A coffee plant usually starts to produce flowers three to four years after it is planted, and it is from these flowers that the fruits of the plant (commonly known as coffee cherries) appear, with the first useful harvest possible around five years after planting. The cherries ripen around eight months after the emergence of the flower, by changing color from green to red, and it is at this time that they should be harvested. In most coffee-growing countries, there is one major harvest a year; though in countries like Colombia, where there are two flowerings a year, there is a main and secondary crop, the main one April to June and a smaller one in November to December.
In most countries, the coffee crop is picked by hand, a labour-intensive and difficult process, though in places like Brazil, where the landscape is relatively flat and the coffee fields are immense, the process has been mechanized.
Wet process
thumb|A field-expedient coffee fermentation tank in Vietnam
In the "wet process", the fruit covering the coffee beans is removed before they are dried. Coffee processed by the wet method is called wet processed or washed coffee. The wet method requires the use of specific equipment and substantial quantities of water.
The coffee cherries are sorted by immersion in water. Bad or unripe fruit will float and the good ripe fruit will sink. The skin of the cherry and some of the pulp is removed by pressing the fruit by machine in water through a screen. The bean will still have a significant amount of the pulp clinging to it that needs to be removed. This is done either by the classic ferment-and-wash method or a newer procedure known either as: machine-assisted wet processing, aquapulping or mechanical demucilaging.
thumb|Sorting coffee in water
In the ferment-and-wash method of wet processing, the remainder of the pulp is removed by breaking down the cellulose by fermenting the beans with microbes and then washing them with large amounts of water. Fermentation can be done with extra water or, in "dry fermentation", in the fruit's own juices only.
The fermentation process has to be carefully monitored to ensure that the coffee does not acquire undesirable, sour flavors. For most coffees, mucilage removal through fermentation takes between 8 and 36 hours, depending on the temperature, thickness of the mucilage layer, and concentration of the enzymes. The end of the fermentation is assessed by feel, as the parchment surrounding the beans loses its slimy texture and acquires a rougher "pebbly" feel. When the fermentation is complete, the coffee is thoroughly washed with clean water in tanks or in special washing machines.
The fermentation process produces wastewater that contains a high organic load, which should be prevented from entering fresh water supplies. In machine-assisted wet processing, fermentation is not used to separate the bean from the remainder of the pulp; rather, this is done through mechanical scrubbing. This process reduce both water use and the generation of wastewater. In addition, removing mucilage by machine is easier and more predictable than removing it by fermenting and washing. However, by eliminating the fermentation step and prematurely separating fruit and bean, mechanical demucilaging can remove an important tool that mill operators have of influencing coffee flavor. Furthermore, the ecological criticism of the ferment-and-wash method increasingly has become moot, since a combination of low-water equipment plus settling tanks allows mill operators to carry out fermentation with limited pollution. The damaged beans are more prominent on lower altitude-grown beans and certain varietals with porous features.
Any wet processing of coffee produces coffee wastewater, which can be a pollutant. Ecologically sensitive farms reprocess the wastewater along with the shell and mucilage as compost to be used in soil fertilization programs. The amount of water used in processing can vary, but most often is used in a 1 to 1 ratio.
After the pulp has been removed, what is left is the bean surrounded by two additional layers: the silver skin and the parchment. The beans must be dried to a water content of about 10% before they are stable. Coffee beans can be dried in the sun or by machine but in most cases it is dried in the sun to 12–13% moisture and brought down to 10% by machine. Drying entirely by machine is normally only done where space is at a premium or the humidity is too high for the beans to dry before mildewing.
thumb|Coffee drying in the sun. Doka Plantation Costa Rica
thumb|Coffee drying in Indonesian drying racks called 'para para'
When dried in the sun, coffee is most often spread out in rows on large patios where it needs to be raked every six hours to promote even drying and prevent the growth of mildew. Some coffee is dried on large raised tables where the coffee is turned by hand. Drying coffee this way has the advantage of allowing air to circulate better around the beans promoting more even drying but increases cost and labor significantly.
After the drying process (in the sun or through machines), the parchment skin or pergamino is thoroughly dry and crumbly, and easily removed in the hulling process. Coffee occasionally is sold and shipped in parchment or en pergamino, but most often a machine called a huller is used to crunch off the parchment skin before the beans are shipped. It may take up to four weeks before the cherries are dried to the optimum moisture content, depending on the weather conditions. On larger plantations, machine-drying is sometimes used to speed up the process. Various types of mechanical driers exist and can be fueled by gas, wood, or sometimes discarded parchment. The technique used to dry coffees mechanically can be viewed similarly to the roasting process; a drying regime can be employed in a way to preserve the quality of the beans.
The drying operation is the most important stage of the process, since it affects the final quality of the green coffee. A coffee that has been overdried will become brittle and produce too many broken beans during hulling (broken beans are considered defective beans). Coffee that has not been dried sufficiently will be too moist and prone to rapid deterioration caused by the attack of 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 90% of the Arabica coffee produced in Brazil, most of the coffees produced in Ethiopia, Haiti and Paraguay, as well as for some Arabicas produced in India and Ecuador. Almost all Robustas are processed by this method. It is not practical in very rainy regions, where the humidity of the atmosphere is too high or where it rains frequently during harvesting. This process is said to reduce acidity and increase body.
The tricky part during the semi-washed process method are bacteria which are always around. Fermentation can start immediately as honey dried coffee beans have a remaining "sugar" layer which is vulnerable to any sort of mold and offers feeding ground for bacteria. Drying carefully and under supervision is crucial to the success of this processing method. The beans need to constantly move during the drying process to prevent mold and fungal infections. The processor needs to rake the green coffee beans 2–3 times per hour to ensure a safe drying process. Once the beans have reached a sufficient moisture level, again, the beans are dry milled to remove the "parchment" layers and are sent off to roasters and wholesalers globally.
Honey processing bridges the gap between washed and natural coffees as it generally possesses some of the body and sweetness of a natural while retaining some of the acidity of a washed. Honey coffees often have a syrupy body with enhanced sweetness, round acidity and earthy undertones.
Milling
thumb|Structure of coffee berry and beans:
The final steps in coffee processing involve removing the last layers of dry skin and remaining fruit residue from the now-dry coffee, and cleaning and sorting it. These steps are often called dry milling to distinguish them from the steps that take place before drying, which collectively are called wet milling.
thumb|Ethiopian women sort coffee beans at a long table.
The final step in the cleaning and sorting procedure is called color sorting, or separating defective beans from sound beans on the basis of color rather than density or size. Color sorting is the trickiest and perhaps most important of all the steps in sorting and cleaning. With most high-quality coffees color sorting is done in the simplest possible way: by hand. Teams of workers pick discolored and other defective beans from the sound beans. The very best coffees may be hand-cleaned twice (double picked) or even three times (triple picked). Coffee that has been cleaned by hand is usually called European preparation; most specialty coffees have been cleaned and sorted in this way. To meet the demand for aged coffee, some product was aged in large, open-sided warehouses at port for six or more months in an attempt to expose the coffee to the same conditions that shipments used to require. Consumers can also elect to buy unroasted coffee to be roasted at home. Green coffee can also be used for the preparation of infusions or ingested as ground powder, but this is of limited relevance to the global coffee market.
References
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