Coffea arabica

Taxonomy

The botanical name Coffea arabica was formally published by Carl Linnaeus in his Species plantarum in 1753. The species had been described and depicted before, as Linnaeus was able to refer to Antoine de Jussieu, who named it Jasminum arabicum, published in 1715, after studying a specimen sent to him from the Botanic Garden of Amsterdam, Gaspard Bauhin's Pinax of 1623 under 'Evonymus IV' and Prospero Alpini's De plantis Aegypti liber, published in 1592.

Coffea arabica is one of the polyploid species of the genus Coffea, as it carries four copies of the eleven chromosomes (44 total) instead of the 2 copies of diploid species. Specifically, Coffea arabica is itself the result of a hybridization between the diploids Coffea canephora and Coffea eugenioides, thus making it an allotetraploid, with two copies of two different genomes. This hybridization event at the origin of Coffea arabica is estimated between 1.08 million and 543,000 years ago and is linked to changing environmental conditions in East Africa.

Distribution and habitat

Endemic to the southwestern highlands of Ethiopia, Coffea arabica is grown in dozens of countries between the Tropic of Capricorn and the Tropic of Cancer. It is commonly used as an understory shrub. It has also been recovered from the Boma Plateau in South Sudan. Coffea arabica is also found on Mount Marsabit in northern Kenya, but it is unclear whether this is a truly native or naturalised occurrence; recent studies support it being naturalised. The species is widely naturalised in areas outside its native land, in many parts of Africa, Latin America, Southeast Asia, India, China, and assorted islands in the Caribbean and in the Pacific.

Arabica coffee typically grows at high elevations with moderate temperatures and well drained soils.The species thrives in tropical climates with consistent rainfall and partial shade.The native habitat is characterized by montane forest with rich biodiversity.

The coffee tree was first brought to Hawaii in 1813, and it began to be extensively grown by about 1850. It was formerly more widely grown, especially in Kona, and it persists after cultivation in many areas. In some valleys, it is a highly invasive weed. In the Udawattakele and Gannoruwa Forest Reserves near Kandy, Sri Lanka, coffee shrubs are also a problematic invasive species.

In Hawaii, coffee cultivation became a major agricultural activity in the 19th century.However, escaped plants have spread beyond plantations and established wild populations. These populations can alter native ecosystems by competing with local plant species.

Coffee has been produced in Queensland and New South Wales of Australia, starting in the 1980s and 1990s. The Wet Tropics Management Authority has classified Coffea arabica as an environmental weed for southeast Queensland due to its invasiveness in non-agricultural areas.

Coffee production in Australia remains relatively small but has expanded in subtropical regions. Environmental concerns have arisen due to its ability to spread into surrounding natural habitats. Management efforts focus on limiting its spread outside cultivated areas.

History

The first written record of coffee made from roasted coffee beans (botanical seeds) comes from Arab scholars, who wrote that it was useful in prolonging their working hours. Yemen and southern Ethiopia were likely pioneering regions for coffee bean cultivation. The Arab innovation in Yemen of making a brew from roasted beans spread first among the Hijazis, Egyptians and Turks, and later found its way around the world. Some scholars believe that the coffee plant was introduced from Yemen, based on a Yemeni tradition that slips of both coffee and qat were planted at Udein ('the two twigs') in Yemen in pre-Islamic times. Arabica coffee production in Indonesia began in 1699 through the spread of Yemen's trade. Indonesian coffees, such as Sumatran and Java, are known for their heavy body and low acidity. These qualities make them ideal for blending with the higher acidity coffees from Central America and East Africa.

Cultivation and use

Coffea arabica accounts for 60% of the world's coffee production.

C. arabica takes approximately seven years to mature fully, and it does best with 1.2–1.8 metres (47–71 in) of rain, evenly distributed throughout the year. It is usually cultivated at an altitude between 1,200 and 1,500 m (3,900 and 4,900 ft), but there are plantations that grow it as low as sea level and as high as 2,800 m (9,200 ft).

The plant can tolerate low temperatures, but not frost, and it does best with an average temperature between 15 and 24 °C (59 and 75 °F). Commercial cultivars mostly only grow to about 5 m, and are frequently trimmed as low as 2 m to facilitate harvesting. Unlike Coffea canephora, C. arabica prefers to be grown in light shade.

Three to four years after planting, C. arabica produces small, white, highly fragrant flowers. The sweet fragrance resembles the sweet smell of jasmine flowers. Flowers opening on sunny days result in the greatest number of berries. This can be problematic and deleterious, however, as coffee plants tend to produce too many berries; this can lead to an inferior harvest and even damage yield in the following years, as the plant will favour the ripening of berries to the detriment of its vegetative growth.

On well-kept plantations, overflowering is prevented by pruning the tree. The flowers last only a few days, leaving behind only the thick, dark-green leaves. The berries then begin to appear. These are as dark green as the foliage until they begin to ripen, but as chlorophyll degrades and anthocyanins buildup, the plant becomes completely red or yellow depending on the variety of C. arabica. At this point, they are called "cherries", which fruit they then resemble, and are ready for picking.

The berries are oblong and about 1 cm long. Inferior coffee results from picking them too early or too late, so many are picked by hand to be able to better select them, as they do not all ripen at the same time. They are sometimes shaken off the tree onto mats, which means ripe and unripe berries are collected together.

The trees are difficult to cultivate and each tree can produce from 0.5 to 5.0 kilograms (1.1 to 11.0 lb) of dried beans, depending on the tree's individual character and the climate that season. The most valuable part of this cash crop is the beans inside. Each berry holds two locules containing the beans. The coffee beans are actually two seeds within the fruit; sometimes, a third seed or one seed, a peaberry, grows in the fruit at the tips of the branches. These seeds are covered in two membranes; the outer one is called the "parchment coat" and the inner one is called the "silver skin".

On Java, trees are planted at all times of the year and are harvested year-round. In parts of Brazil, however, the trees have a season and are harvested only in winter. The plants are vulnerable to damage in such poor growing conditions as cold or low pH soil, and they are also more vulnerable to pests than the C. robusta plant.

It is expected that a medium-term depletion of indigenous populations of C. arabica may occur, due to projected global warming, based on IPCC modelling. Climate change—rising temperatures, longer droughts, and excessive rainfall—appears to threaten the sustainability of arabica coffee production, leading to attempts to breed new cultivars for the changing conditions.

Gourmet coffees are almost exclusively high-quality mild varieties of arabica coffee, and among the best known arabica coffee beans in the world are those from Jamaican Blue Mountain, Colombian Supremo, Tarrazú, Costa Rica, Guatemalan Antigua, and Ethiopian Sidamo.

Blends consisting only of Arabica are often labelled "100% Arabica" as a sign of quality. In 2023, several large coffee roasters dropped the "100% Arabica" declaration previously residing on some of their packages and started to blend less expensive Robusta coffee into the mix. To avoid making larger changes to the visual design of the package the Arabica label was replaced by other labeling, keeping the previous ornamental design, thereby presenting a case of shrinkflation. In some case, the coffee is still advertised as "100% Arabica" in flyers in 2024, but is no longer declared so on the actual package.

Strains

One strain of Coffea arabica (called AC1, AC2 and AC3 in honour of the geneticist Alcides Carvalho) naturally contains very little caffeine. While beans of normal C. arabica plants contain 12 mg of caffeine per gram of dry mass, these mutants contain only 0.76 mg of caffeine per gram, with similar expected cup quality.

Threats

Although it has a huge wild population of 13.5 to 19.5 billion individuals throughout its native range, C. arabica is still assessed as endangered on the IUCN Red List due to numerous threats it faces. Because it is an understory plant, it needs standing forest, making it highly susceptible to the historically significant deforestation levels in Ethiopia; before major deforestation, forest cover was thought to be between 25–31% of Ethiopia's total land surface, but has dropped to just 4%, and deforestation still continues. In addition, climate change may have a major effect on growing areas for wild C. arabica in Ethiopia due to its high-temperature sensitivity, and estimates indicate that population could reduce by 50–80% with a 40–50% reduction in area of occupancy by 2088; climate change can also impact reproductive success. In addition, the main pest of coffee, the coffee berry borer (Hypothenemus hampei) may benefit from climate change and colonize higher altitudes that were formerly too cold for it, which can also affect coffee populations.

Additionally, coffee leaf rust caused by the fungus Hemileia vastatrix is a major threat to the supply of Coffea arabica causing losses of up to $2 billion US dollars annually. From 2012 to 2013 Hemileia vastatrix was responsible for a 16% decrease in production of Coffea arabica across Central America. The fungus destroys the plant by causing rapid defoliation, which hinders the plant from performing photosynthesis.

The conservation of the genetic variation of C. arabica relies on conserving healthy populations of wild coffee in the Afromontane rainforests of Yemen. Genetic research has shown coffee cultivation is threatening the genetic integrity of wild coffee because it exposes wild genotypes to cultivars. Nearly all of the coffee that has been cultivated over the past few centuries originated from just a handful of wild plants from Yemen, and the coffee growing on plantations around the world contains less than 1% of the diversity in the wilds of Yemen alone.

Climate change also serves as a threat to cultivated C. arabica due to their temperature sensitivity, and some studies estimate that by 2050, over half of the land used for cultivating coffee could be unproductive. The more heat-tolerant Coffea stenophylla may replace C. arabica as the dominant coffee species in cultivation in order to guard against this.