Arabica coffee

Arabica coffee is a small evergreen tree or large shrub, 4–8 m tall in cultivation (up to 15 m in the wild), with opposite branching. The leaves are opposite, simple, ovate to elliptic, leathery and glossy, 10–15 cm long, with slightly wavy margins and stipules at the nodes. The flowers are bisexual, white and fragrant, usually 5-merous, borne in clusters of 2–4 in the leaf axils; the tree is mainly self-pollinating (about 90%), which makes populations genetically fairly uniform. The fruit is a drupe (the 'cherry'), ellipsoid and about 1.5 cm long, turning from green through yellow to red when ripe, usually containing two flat seeds (beans) each with a central groove on the flat face. The roots are shallow and fibrous, so the plant needs loose, organic-rich soil. Coffea arabica is an allotetraploid with 2n = 4x = 44.

According to Kew POWO the native range of Coffea arabica is E. South Sudan (Boma Plateau), SW. Ethiopia and N. Kenya (Mt. Marsabit), growing in humid evergreen forest and seasonally dry tropical habitat at roughly 1,000–2,000 m. The centre of origin and diversity is the highland forest of southwestern Ethiopia, South Sudan and northern Kenya; because the species is largely self-pollinating its genetic diversity is naturally low. From the 14th century coffee seeds were carried from Ethiopia to Yemen, where cultivation expanded and became a secondary centre of dispersal worldwide through the Typica and Bourbon lineages (Scalabrin et al., 2020). Coffee reached Vietnam in the 19th century under French rule and now centres on the Central Highlands (Dak Lak, Lam Dong, Gia Lai, Dak Nong) and Son La; Vietnam is the world's second-largest coffee exporter, mainly robusta, while arabica is concentrated in Lam Dong, Son La and Dien Bien. Brazil is the largest coffee producer, followed by Colombia, Vietnam, Indonesia and Ethiopia.

Chemically, the arabica bean contains more than 1,000 compounds, whose core functional groups are caffeine, chlorogenic acids (CGAs), trigonelline, the diterpenes cafestol and kahweol, and roast-derived melanoidins. Caffeine is a methylxanthine making up about 1.2–1.5% of the dry weight of arabica (lower than robusta – Coffea canephora, at 1.7–4%). Chlorogenic acids are a polyphenol group forming 5–8% of dry weight, with 5-O-caffeoylquinic acid (5-CQA) predominant (36–40% of total CGAs); about one third of ingested 5-CQA reaches the systemic circulation, peaking in plasma within 0.5–1.5 h. Trigonelline is the characteristic alkaloid (about 1% of dry weight), contributing to roast aroma and showing anti-diabetic potential. The diterpenes cafestol and kahweol are abundant in unfiltered coffee (espresso, French press) and can raise blood cholesterol. During roasting, Maillard reactions generate melanoidins and aroma compounds (pyrazines, furans, lactones) while reducing CGAs. Green beans also contain protein (~11%), lipids (~12%), carbohydrates and minerals (potassium, magnesium).

Coffee is one of the world's most popular drinks: roasted beans are brewed as espresso, phin or filter coffee; they flavour cakes, confectionery and ice cream; caffeine is extracted for energy drinks and medicines; coffee leaves are used as a polyphenol-rich 'coffee-leaf tea'; and spent grounds go into exfoliants, compost and growing media. In research, a review (PMC, 2024) summarised the effects of coffee's core functional components (caffeine, trigonelline, CGAs, cafestol, kahweol, melanoidins): CGAs activate the antioxidant Nrf2 pathway and inhibit α-glucosidase to modulate postprandial glycaemia, and a 9-year follow-up linked coffee drinking to lower risk of Alzheimer's-related dementia (ADRD) and Parkinson's disease. Caffeine content per serving ranges from 48 to 317 mg (Ludwig et al., 2014). Koshiro et al. (2006) analysed changes in caffeine and trigonelline during fruit ripening, and de Andrade et al. (2023) showed that both caffeine and trigonelline play antioxidant roles. The allotetraploid genome of C. arabica has been sequenced (Salojärvi et al., Nature Genetics, 2024).

On safety, according to the European Food Safety Authority (EFSA, 2015) healthy adults can take up to 400 mg caffeine a day (single doses up to 200 mg); pregnant women should limit intake to 200 mg/day and children to 3 mg/kg/day. Heavy intake of unfiltered coffee (espresso, French press) can raise LDL cholesterol because of cafestol and kahweol. Coffee can cause anxiety, insomnia and palpitations in sensitive people and interacts with some medicines; roasting forms acrylamide and green beans may carry ochratoxin A (quality control needed). Epidemiological research shows that moderate intake of 3–4 cups a day (300–400 mg caffeine) carries little risk and may be beneficial (Higdon & Frei, 2006); IARC (2016) classifies coffee in Group 3 (not classifiable as to carcinogenicity), while very hot drinks above 65 °C are Group 2A. On conservation, the International Union for Conservation of Nature (IUCN) lists Coffea arabica as Endangered (EN) in its 2020 assessment (Moat et al., e.T18289789) because climate change sharply contracts the suitable habitat of wild populations; Kew POWO also records a provisional Vulnerable (VU) assessment. The main risks are climate change, deforestation, coffee leaf rust (the fungus Hemileia vastatrix) and the narrow genetic base that stems from a single polyploidisation event. Conservation priorities are to protect wild populations in Ethiopia, South Sudan, Kenya and Yemen and to maintain genebanks (such as CATIE and World Coffee Research).