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| The Aroma of Coffee (Compound Interest) |
What is it about that delicious smell of coffee? Or, more specifically, what lies behind it? The graphic above takes a look at a selection of the chemical compounds behind this aroma.
So that's the chemistry, but what about the biology of coffee?
Several species of shrub of the genus Coffea produce the
berries from which coffee is extracted. The two main species commercially
cultivated are Coffea canephora (predominantly a form known as 'robusta') and
C. arabica. C. arabica, the most highly regarded species, is native to the
southwestern highlands of Ethiopia and the Boma Plateau in southeastern Sudan
and possibly Mount Marsabit in northern Kenya. C. canephora is native to western
and central Subsaharan Africa, from Guinea to Uganda and southern Sudan. Less
popular species are C. liberica, C. stenophylla, C. mauritiana, and C.
racemosa.
All coffee plants are classified in the large family
Rubiaceae. They are evergreen shrubs or trees that may grow 5 m (15 ft) tall
when unpruned. The leaves are dark green and glossy, usually 10–15 cm (4–6 in)
long and 6 cm (2.4 in) wide, simple, entire, and opposite. Petioles of opposite
leaves fuse at base to form interpetiolar stipules, characteristic of
Rubiaceae. The flowers are axillary, and clusters of fragrant white flowers
bloom simultaneously. Gynoecium consists of inferior ovary, also characteristic
of Rubiaceae. The flowers are followed by oval berries of about 1.5 cm (0.6
in). When immature they are green, and they ripen to yellow, then crimson,
before turning black on drying. Each berry usually contains two seeds, but
5–10% of the berries have only one; these are called peaberries.
Arabica
berries ripen in six to eight months, while robusta take nine to eleven months.
Coffea arabica is predominantly self-pollinating, and as a
result the seedlings are generally uniform and vary little from their parents.
In contrast, Coffea canephora, and C. liberica are self-incompatible and
require outcrossing. This means that useful forms and hybrids must be
propagated vegetatively. Cuttings, grafting, and budding are the usual methods
of vegetative propagation. On the other hand, there is great scope for
experimentation in search of potential new strains.
In 2016, Oregon State University entomologist George Poinar,
Jr. announced the discovery of a new plant species that's a 45-million-year-old
relative of coffee found in amber. Named Strychnos electri, after the Greek word
for amber (electron), the flowers represent the first-ever fossils of an
asterid, which is a family of flowering plants that not only later gave us
coffee, but also sunflowers, peppers, potatoes, mint — and deadly poisons.
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