Coffee production

For the process of turning coffee beans into a beverage, see Coffee preparation.

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

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. Whether picked by hand or by machine, all coffee is harvested in one of two ways:

Mechanical strippers used for coffee fruit harvesting

Strip picked

All coffee fruit is removed from the tree, regardless of maturation state. This can either be done by machine or by hand. In the first method, pickers generally place a canvas on the ground. They then grab the branch next to the trunk with their hands and pull outward, knocking all of the fruit onto the ground. After doing this with all branches and trees for the length of the canvas, the pickers then collect the coffee in bags. This process can be facilitated through the use of mechanical strippers.

Selectively picked

Only the ripe cherries are harvested and they are picked individually by hand. Pickers rotate among the trees every eight to ten days, choosing only the cherries which are at the peak of ripeness. It usually takes two to four years after planting for a coffee plant to produce coffee beans that are ripe enough to harvest. The plant eventually grows small white blossoms that drop and are replaced by green berries. These green berries will become a deep red color as they ripen. It takes about 9 months for the green cherries to reach their deepest red color. Because this kind of harvest is labor-intensive, and thus more costly, it is used primarily to harvest the finer arabica beans.

Workers pulping coffee beans in Guatemala

Depending on the grower, coffee pickers are sometimes specifically instructed to not pick green coffee berries since the seeds in the berries are not fully formed or mature. Workers who pick coffee by hand are generally paid a piece rate based on the weight or volume of cherries collected, or a daily wage.

Piecework and daily payment predominate on Colombian farms. In a 2016 survey of 7,578 coffee pickers by the National Federation of Coffee Growers, half were paid by the kilogram collected, 37.5 percent received a daily wage, 11 percent were unpaid family workers and 1.5 percent were employees; piecework rates ranged from US$0.02 to US$0.21 per kilogram and the average daily wage was US$6.70, with men earning about 12 percent more than women.

Smallholders in Ethiopia and Uganda mostly hire casual labor paid by task or piece rate during the harvest peak, and what a picker earns in a day depends not only on the rate but on how much ripe fruit the trees carry. Harvesters at sites dominated by Fairtrade-certified producers in those two countries received piece rates about 20 percent lower than elsewhere and earned less per day. On farms in Latin America, piece rates are often combined with production quotas for tasks such as weeding and fertilizing. The labor-rights organization Verité has argued that piece-rate pay does not guarantee the legal minimum wage, and that where controls are weak it goes together with unpaid overtime and with child labor, as families bring children to the fields to meet quotas.

A 2020 International Labour Organization study of five major producing countries found that coffee workers earned less than the national average wage, and less than the average agricultural wage, in every country examined. Median monthly earnings for employees were roughly US$20 in Ethiopia, $76 in Indonesia, $110 in India, $116 in Vietnam and $350 in Costa Rica, in 2020 dollars. An estimated 45 percent of coffee employees in Costa Rica and 91 percent in Indonesia earned less than the legal minimum wage; Ethiopia has no minimum wage. Women earned substantially less than men. In a 2025 focus-group study of workers on specialty coffee farms in Honduras and El Salvador, participants said their daily wages were no higher, and sometimes lower, than on conventional farms, though longer periods of employment could raise their annual income. Several complained that the price premiums growers received for specialty coffee were not passed on to workers.

Lots including unripe coffee fruit are often used to produce cheaper mass consumer coffee beans, which are characterized by a displeasingly bitter/astringent flavor and a sharp odor. Red berries, with their higher aromatic oil and lower organic acid content, are more fragrant, smooth, and mellow. As such, coffee picking is one of the most important stages in coffee production.

Wet process

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.

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 two give noticeably different results, underwater fermentation being said to emphasise acidity and aroma and to suppress some astringency.

How much oxygen the fermentation gets is a further variable. In the Indonesian Labu method the pulped fruit is sealed into polypropylene bags with as much air as possible expelled, so that anaerobic organisms dominate and produce secondary metabolites unlike those of an open tank; fermentation takes correspondingly longer and the bags must be turned. The cup is described as tasting of wild red fruit, with a sharp acidity. The authors of The Craft and Science of Coffee draw an explicit parallel with winemaking, where fermentation is likewise decisive, and suggest coffee has yet to follow it in replacing simple tanks with vessels in which temperature, pH, oxygen and microbiota are all controlled.

Fermentation has to be watched closely, or the coffee turns sour. How long it takes depends on the temperature, the thickness of the mucilage layer and the concentration of the enzymes at work; published figures run from about twelve hours to thirty-six. Millers judge the end point by touch, the parchment losing its slimy coating and turning gritty underneath the fingers. The coffee is then washed thoroughly in clean water, in tanks or in purpose-built washing machines. 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 reduces both water use and the generation of wastewater. Mechanical demucilaging gives a more consistent result than fermentation, because every bean receives the same treatment, and it avoids the 2 to 3 per cent loss of weight that fermentation causes. The two methods do not taste the same: mechanically demucilaged beans are generally described as having a sharper acidity, and fermented beans a juicier and finer one. Rinsing the beans before drying improves the quality of mechanically demucilaged coffee.

Low-water milling equipment involves trade-offs of its own. As less water is used, damage to the parchment and the beans tends to increase, more parchment is lost with the pulp and more pulp is left mixed with the parchment, which in turn affects fermentation and cup quality; reducing water consumption is also harder in large mills than in small ones. Conveying the coffee dry, on elevators and belts rather than in water channels, is an alternative to reducing the water in the mill itself.

Mucilage removal is the only stage of the wet process that requires water, and it is the source of the coffee wastewater. Using less water does not lessen the pollution so much as concentrate it: the lower the water consumption, the higher the organic load of the effluent. Ecologically sensitive farms reprocess the wastewater along with the shell and mucilage as compost to be used in soil fertilization programs. Dried mucilage recovered from mill wastewater has useful fertilising properties, and nitrogen-rich coffee pulp can replace artificial fertiliser on the plantation. 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. Washed coffee leaves the mill at about 53 per cent moisture, and must be dried to 10–12 per cent on a wet basis before it is stable. At that level the water activity of the bean falls to about 0.65–0.68, below the 0.77–0.83 needed for Aspergillus ochraceus to grow and well below the 0.83–0.87 at which it produces ochratoxin A. Coffee above 12 per cent moisture may be rejected at the buying station. Drying is a critical stage, because poor drying can undo the quality achieved at every earlier step.

Coffee beans can be dried in the sun or by machine. Mechanical drying takes hours where sun drying takes days, and the two do not give the same cup: the long sun-drying period can cause the seed to begin germinating, which is held to give a more desirable flavour. 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.

Coffee drying in the sun. Doka Plantation Costa Rica

Coffee beans drying. Drying racks are called 'para para' in Indonesia

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.

Dry process

Dry process, also known as unwashed or natural coffee, is the oldest method of processing coffee. The whole fruit is cleaned after harvest and then dried in the sun, on trestle tables or spread thinly across a patio.

Before drying begins the crop is graded and cleaned, so that unripe, overripe and damaged fruit is set aside along with soil, twigs, leaves and other field debris. Hand winnowing over a wide sieve does most of this work, and whatever the draught fails to carry off is picked off the mesh. Flotation in a water channel beside the drying ground can be used to the same end.

The fruit is laid out in the sun, on concrete or brick patios or on waist-height trestle beds of matting, and is turned by hand or with rakes so that it dries evenly. Sun drying on patios is the cheapest and most energy-efficient method, though rain and excessively strong sunlight can both spoil the crop. Depending on the weather, four weeks may pass before the fruit reaches the maximum moisture content of 12.5 per cent. Larger plantations sometimes finish the job in machine driers, after the coffee has been pre-dried in the sun for a few days. 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.

Drying governs the final quality of the green bean more than any other stage. Taken too far, the coffee turns brittle and shatters in the huller, and broken beans count as defects; stopped too early, the moisture left behind opens the crop to fungal and bacterial spoilage.

Once dry, the fruit is held in bulk silos until it goes to the mill for hulling, sorting, grading and bagging, where a single pass through the hulling machine strips every outer layer at once.

Around 90 per cent of Brazilian arabica is handled this way, as is most coffee from Ethiopia, Haiti and Paraguay and part of the arabica crop of India and Ecuador; nearly all robusta is dry-processed. The method depends on dry harvest weather, and is impractical where the air stays humid or rain falls often during picking.

Semi-dry process

Two distinct methods fall between the wet and dry processes and are often grouped together as semi-dry or semi-washed. In both, the outer skin is removed as in wet processing, but the later steps differ.

Pulped natural or honey process

The skin is removed and the mucilage is left on the parchment; the beans are fermented and dried with it in place, and the washing step is omitted. Depending on how much mucilage is retained, the result is described as yellow, red or black honey. Yellow honey, from which part of the mucilage has been removed mechanically, dries in about eight to ten days; red honey retains roughly half to three quarters of the mucilage and takes twelve to fifteen; black honey is dried with all of it and takes around thirty days, needing frequent turning to stop the beans sticking together, which makes it the most demanding of the three. The method was first tried at the Instituto Agronômico de Campinas in Brazil in the early 1950s and taken up commercially by farmers in southern Minas Gerais in the 1980s; the Brazilian product is known as cereja descascado. The process uses considerably less water than the wet method, and the cup is typically described as mellow and sweet, with mild acidity and fruit or honey notes. Sugars and other compounds from the retained mucilage migrate into the beans during the long fermentation, which a study of honey-processed robusta identified as the source of its distinct flavor.

Wet-hulled process

Wet hulling, known in Indonesia as giling basah ("wet grinding"), is used by smallholders in Sumatra, Sulawesi, Flores and Papua. Its distinctive feature is that the parchment is removed while the bean is still wet, rather than after drying. The practice is a response to Indonesia's climate: the rainy season coincides with the harvest, drying can otherwise take two to three weeks, and the coffee has to be dried quickly to prevent mould. Hulling the parchment while the bean is still soft and damp is difficult, and the pressure in the hulling chamber increases the risk of bruised beans. In the Mandheling coffee region around Lake Toba, farmers pulp the cherries by hand on the day of harvest, ferment the beans overnight, wash them, and sun-dry the parchment for between half a day and two days before selling it, still wet, to local traders. The traders hull the parchment at 40–45 percent moisture using modified Engelberg hullers, and the exposed beans are then sun-dried for three to five days to 14–17 percent moisture before exporters dry them further to about 13 percent. The cup produced this way is characterized by low acidity, heavy body, and spicy, earthy and fruity notes. Because the coffee is handled wet for longer than in other methods, and wet parchment is sometimes stored for days or weeks before hulling, the process carries a risk of mold growth. A 2005 study of Mandheling coffee found Aspergillus molds on stored wet parchment and detected ochratoxin A in five of 42 samples, at levels well below the European Union limit.

Milling

Structure of coffee berry and beans:

1. center cut
2. bean (endosperm)
3. silver skin (testa, epidermis)
4. parchment (hull, endocarp)
5. pectin layer
6. pulp (mesocarp)
7. outer skin (pericarp, exocarp)

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 stages are common to both wet- and dry-processed coffee and are usually carried out at a dedicated plant shortly before the coffee is sold for export; the International Coffee Organization calls them curing. In the trade they are more often called dry milling, as against the wet milling that precedes drying.

Hulling

The first step in dry milling is the removal of what is left of the fruit from the bean, whether it is the crumbly parchment skin of wet-processed coffee, the parchment skin and dried mucilage of semi-dry-processed coffee, or the entire dry, leathery fruit covering of the dry-processed coffee. Hulling is done with the help of machines, which can range from simple millstones to sophisticated machines that gently whack at the coffee.

Polishing

This is an optional process in which any silver skin that remains on the beans after hulling is removed in a polishing machine. This is done to improve the appearance of green coffee beans and eliminate a byproduct of roasting called chaff. It is described by some to be detrimental to the taste because it raises the temperature of the bean through friction, which changes the chemical makeup of the bean.

Cleaning and sorting

Most fine coffee goes through a battery of machines that sort the coffee by the density of bean and by bean size, all the while removing sticks, rocks, nails, and miscellaneous debris that may have become mixed with the coffee during drying. First machines blow the beans into the air; those that fall into bins closest to the air source are heaviest and biggest; the lightest (and likely defective) beans plus chaff are blown in the farthest bin. Other machines shake the beans through a series of sieves, sorting them by size. Finally, a machine called a gravity separator shakes the sized beans on a tilted table, so that the heaviest, densest and best vibrate to one side of the pulsating table, and the lightest to the other.

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.

Color sorting can also be done by machine. Optical sorters pass a stream of beans one at a time in front of sensors calibrated to detect defective beans by brightness or color, and a jet of compressed air ejects each rejected bean from the stream. Machines work best on beans that have already been graded by size and density. Whether the final sorting is done by hand or by machine depends largely on the cost of labor. Hand sorting "is still performed in a few countries in order to maintain employment or because labor is still inexpensive", according to the processing engineer Carlos Brando, while the coffee writer Kenneth Davids describes electronic sorters as essential where wages are high, as in Brazil and Hawaii.

The labor saving can be large. In a study of hill-tribe coffee in northern Thailand, replacing manual sorting of coffee cherries with an optical sorter raised throughput from 25 to 37.5 kilograms per worker-hour to 150 to 500 kilograms per hour per machine, and cut the labor cost of sorting by roughly three quarters. In the primary processing factories of Ethiopia and Tanzania, the final hand-picking of discolored beans is done by women. A 2021 review of occupational dust exposure in these factories found that the hand pickers were less exposed than the male production workers, but still had higher dust exposure and more respiratory symptoms than unexposed controls.

Grading

See also: Single-origin coffee

A man takes a sample of coffee beans from bags in an Ethiopian warehouse for grading.

Grading is the process of categorizing coffee beans by various criteria such as size of the bean, where and at what altitude it was grown, how it was prepared and picked, and how good it tastes (cup quality). Coffees also may be graded by the number of imperfections (broken, under-ripe, or otherwise defective beans; pebbles; sticks; etc.) per sample. For the finest coffees, origin of the beans (farm or estate, region, cooperative) is especially important. Growers of premium estate or cooperative coffees may impose a level of quality control that goes well beyond conventionally defined grading criteria, as this allows their coffee to command the higher price that goes with recognition of consistent quality.

Other steps

Aging

Monsooned Malabar arabica, an "aged" green bean from India, compared with the much darker Yirgachefe beans from Ethiopia

All coffee when it was introduced in Europe came from the port of Mocha in what is now Yemen. Importing the beans to Europe required a lengthy sea voyage around the Horn of Africa, which ultimately changed the coffee's flavor due to age and exposure to saline air. Coffee later spread to India and Indonesia but still required a long sea voyage. Once the Suez Canal was opened, shipment time to Europe was greatly reduced and coffee with flavor less affected by salt and age began arriving. This fresher coffee was, to some degree, rejected as Europeans had not developed a taste for unaged coffee. 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.

India's Monsooned Malabar coffee is the surviving commercial form of this effect. According to the account given in The Craft and Science of Coffee, a consignment shipped from the Malabar Coast to Scandinavia in about 1850 spent more than six months at sea, and the beans absorbed moisture through the ship's wooden holds on the passage round the Cape of Good Hope; they swelled, roughly doubled in size, lost weight, turned from blue-grey to a creamy golden yellow, and arrived tasting quite different. Scandinavian buyers acquired a taste for them. When faster shipping and better packing later removed the effect, those buyers complained that the coffee was wrong, and an Indian investigation established that the change had happened during the voyage. The process was then reproduced deliberately on the west coast of India, producing the monsooned Malabar and Basanally coffees, which India launched on the international market in 1972.

Monsooning is now carried out between June and October, when the southwest monsoon reaches the west coast. Selected large-bean natural coffees are spread in a thick layer on the floor of a well-ventilated warehouse and raked regularly for over a week in the moist, salt-laden wind; once they have swollen and paled, they are bagged, stacked in rows and exposed for a further week, then spread out again, the cycle repeating until the beans reach the golden colour that marks the finished product. They end at around 13 to 14 per cent moisture — high enough that mould would normally be expected. The authors note that no such damage occurs, but describe the explanation, that salt from the seawater acts as a preservative, as presumed rather than scientifically established.

Although it is still widely debated and subject to personal taste, certain types of green coffee are believed to improve with age – especially strains valued for their low acidity, such as beans from Indonesia or India. Several coffee producers sell purposely aged beans, some aging for as long as eight years. However, coffee experts consensus is that a green coffee peaks in flavor and freshness within one year of harvest and that over-aged coffee beans lose much of their essential oil content.

Decaffeination

Main article: Decaffeination

Decaffeination is the process of extracting caffeine from green coffee beans prior to roasting. The most common decaffeination process used in the United States is supercritical carbon dioxide (CO₂) extraction. In this process, moistened green coffee beans are contacted with large quantities of supercritical CO₂ (CO₂ maintained at a pressure of about 4,000 pounds force per square inch (28 MPa) and temperatures between 90 and 100 °C (194 and 212 °F)), which removes about 97% of the caffeine from the beans. The caffeine is then recovered from the CO₂, typically using an activated carbon adsorption system.

Another commonly used method is solvent extraction, typically using oil (extracted from roasted coffee) or ethyl acetate as a solvent. In this process, solvent is added to moistened green coffee beans to extract most of the caffeine from the beans. After the beans are removed from the solvent, they are steam-stripped to remove any residual solvent. The caffeine is then recovered from the solvent, and the solvent is re-used. The Swiss Water Process is also used for decaffeination. Decaffeinated coffee beans have a residual caffeine content of about 0.1% on a dry basis. Not all facilities have decaffeination operations, and decaffeinated green coffee beans are purchased by many facilities that produce decaffeinated coffee.

Storage

Main article: Coffee bean storage

Green coffee stored in bags

Green coffee is usually transported in jute bags or woven poly bags. While green coffee may be usable for several years, it is vulnerable to quality degradation based on how it is stored. Jute bags are extremely porous, exposing the coffee to whatever elements it is surrounded by. Coffee that is poorly stored may develop a burlap-like taste known as "bagginess", and its positive qualities may fade.

In recent years, the specialty coffee market has begun to utilize enhanced storage methods. A gas barrier liner to jute bags is sometimes used to preserve the quality of green coffee. Less frequently, green coffee is stored in vacuum packaging; while vacuum packs further reduce the ability of green coffee to interact with oxygen at atmospheric moisture, it is a significantly more expensive storage option.

Roasting

Main article: Coffee roasting

See also: Home roasting coffee

Although not considered part of the processing pipeline proper, nearly all coffee sold to consumers throughout the world is sold as roasted coffee in general one of four degrees of roasting: light, medium, medium-dark, and dark. 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

Bibliography

• Clarke RJ, Macrae R, eds. (1987). Coffee. Vol. 2: Technology. Barking, Essex: Elsevier Applied Science. ISBN 1-85166-034-8.