Within the plant genus Coffea, two varieties, in particular, play the main role as the basis of the popular hot drink: Coffea arabica and Coffee canephora. More well-known are the two trivial names Arabica and Robusta. The roasted seeds of the two Coffea plants and a few other species in small proportions are the basis for the ground coffee powder. What is the botanical difference between the species, and why is Robusta often called the ugly sister of arabica?
The plant genus Coffea
Coffee – botanically known as Coffea – belongs to the plant family of the Rubiaceae, the reddish plants. Within this plant family, which comprises over 6000 species, two species have gained economic importance as plantation plants: Coffea arabica and Coffea canephora. Arabica accounts for over 60% of global coffee production. Both Coffea species form evergreen trees or shrubs. They have paired leaves and form inflorescences with many flowers. Their fruits are drupes, also known as coffee cherries or coffee berries. The fruits have a sweet taste with little pulp and are surrounded by a thick skin. Under two other layers lies the seed. One fruit usually encloses two seeds. These are the coffee beans. Pearl beans contain only one seed. The basis for the beverage coffee is only created by further processing through various types of drying, fermentation, and roasting.
This type of coffee is known as highland, mountain, or Java coffee. It is believed to be a hybrid of Coffea canephora and Coffea eugenioides. The genetic ancestors of up to 5 m high trees are said to come from Java. Probably the first hybridization was carried out in South Sudan. The grafted coffee plant has 44 chromosomes. It prefers a moderate climate between 15 and 25 °C. It is a deep-rooting plant, and the coffee plants should be planted at a distance of 1.5 m. They are located at an altitude of between 400-2100 meters, and, because of their deep roots, they can survive with less rainfall of between 1500-2500 mm. They can also grow in soils that have a dry upper layer of soil. After rainfall, the coffee plant regularly produces a flower, so that it can be planted mainly in regions with clearly defined rainy seasons. It takes nine months from flowering to fruit ripeness. The beans have an oil content of between 15 and 17%. The sugar content, which is decisive for the acidity and texture of the finished coffee drink, is between 6 and 9%. The main areas of cultivation are in Africa, Central America, and Asia between the 23rd degree north and 25th degree south latitude. If these coffee plants are cultivated at too low an altitude at too high temperatures, they are susceptible to the pest coffee rust, among other things. Overall, it is more sensitive than Robusta.
The lowland coffee plant can grow into trees up to 8 m high. Cultivated Robusta plants are kept small so that they can be harvested easily. Coffea canephora has only 22 chromosomes, is a shallow rooting plant, and is planted at 2 m intervals per plant. This coffee plant thrives at high temperatures between 20-30 °C. It needs higher rainfall between 2000 and 3000 mm. The flowering period is not very predictable. This is also due to the cultivation of humid, unstable climates. It takes 10-11 months from flowering to fruit ripening. In cultivated plants, shortened flowering periods of only six months are possible with a high yield. The oil content of the beans is between 10 and 12 %. The sugar content is in the range of 3-7 %. Therefore, Coffea canephora is less sweet and more bitter, especially in the aftertaste. Canephora owes its trivial name Robusta to its increased resistance to pests, which is due to its high caffeine content of up to 4%. The main cultivation area for Coffea canephora is Vietnam. The coffee plant does not tolerate cold temperatures, so it only thrives around the equator at the 20th parallel.
Due to its refinement, milder taste, and better digestibility, highland coffee is more sought after than Robusta. The statement of the “ugly sister” also refers to this. In many cases, both types are mixed in one coffee. The type of coffee plant does not in itself say anything about the quality of coffee, as many other aspects such as fermentation and roasting, are essential.