The coffee tree is a tropical evergreen shrub (genus Coffea) and grows between the Tropics of Cancer and Capricorn. The two most commercially important species grown are varieties of Coffea arabica (Arabicas) and Coffea canephora (Robustas).
The average Arabica plant is a large bush with dark-green oval leaves. The fruits, or cherries, are rounded and mature in 7 to 9 months; they usually contain two flat seeds, the coffee beans. When only one bean develops it is called a peaberry.
Robusta is a robust shrub or small tree that grows up to 10 metres high. The fruits are rounded and take up to 11 months to mature; the seeds are oval in shape and smaller than Arabica seeds.
Ideal average temperatures range between 15 to 24ºC for Arabica coffee and 24 to 30ºC for Robusta, which can flourish in hotter, harsher conditions. Coffee needs an annual rainfall of 1500 to 3000 mm, with Arabica needing less than other species. Whereas Robusta coffee can be grown between sea-level and about 800 metres, Arabica does best at higher altitudes and is often grown in hilly areas.
Harvesting
As coffee is often grown in mountainous areas, widespread use of mechanical harvesters is not possible and the ripe coffee cherries are usually picked by hand. The main exception is Brazil, where the relatively flat landscape and immense size of the coffee fields allow for machinery use.
Coffee trees yield an average of 2 to 4 kilos of cherries and a good picker can harvest 45 to 90 kilos of coffee cherry per day; this will produce nine to 18 kilos of coffee beans.
Coffee is harvested in one of two ways:
Strip Picked – all the cherries are stripped off of the branch at one time, either by machine or by hand.
Selectively Picked – only the ripe cherries are harvested and they are picked by hand.
Pickers check the trees every 8 to 10 days and individually pick only the fully ripe cherries. This method is labour intensive and more costly. Selective picking is primarily used for the finer Arabica beans.
After harvesting the next step is to remove the coffee seeds from the ripe fruit and dry them. This can be done in two ways: the dry and the wet methods.
The Dry Method
The dry or ‘natural’ method involves drying the whole cherry. It is the oldest, simplest method and requires little machinery. The harvested cherries are sorted and cleaned, by hand, to remove unripe, overripe and damaged cherries as well as any dirt, soil, twigs and leaves. This can also be done by floating the cherries in water.
The coffee cherries are spread out in the sun, either on large concrete or brick patios, or on matting raised to waist height on trestles. If it rains they are covered up. As the cherries dry, they are raked or turned by hand to ensure even drying. It can take up to 4 weeks before the cherries are dried sufficiently. On larger plantations, machine-drying is sometimes used to speed up the process after the coffee has been pre-dried in the sun for a few days.
Dried cherries are brittle with a hard outer shell and should have a maximum moisture content of 12.5%. The dried cherries are stored in silos until they are sent to the mill for hulling, where the outer layers of the dried cherry are removed. The ‘green coffee’ beans are then sorted and graded ready for selling.
Almost all Robustas are processed by this method. Almost all the Robustas as processed by this method. The dry method is used for the majority of the Arabica coffee produced in Brazil, most of the coffees produced in Ethiopia, Haiti and Paraguay, and some Arabicas from India and Ecuador.
The Wet Method
The wet method requires the use of special equipment and the availability of water. As with the dry method, the ripe cherries are first cleaned. They are then pulped by a machine that squeezes the cherries so that the flesh and the skin are separated from the beans. The beans are left with a slippery outer skin (the mucilage) and a parchment covering.
The beans are further cleaned to remove lingering bits of pulp and put in large tanks; there the mucilage is broken down by natural enzymes and washed away. This takes between 24 and 36 hours. Then the coffee is thoroughly washed with clean water. At this point the coffee is approximately 57% moisture.
To reduce the moisture to a desirable maximum of 12.5%, the parchment coffee is dried either in the sun, in a mechanical dryer, or by a combination of both. Sun-drying takes from 8 to 10 days. This parchment coffee is then stored.
Just before sale, this coffee is hulled to remove the parchment, and cleaned, screened, sorted and graded. This ‘green coffee’ is now ready for selling.
During roasting, the characteristic coffee taste aroma components are formed, along with the typical brown colour of the beans. More than 1000 different aroma components of coffee are known. By variation of the roasting conditions it is possible to achieve the specific flavor profile of the final coffee according to the preferences of the consumer. Green coffee beans are heated to between 180ºC and 240ºC for 1.5 to 20 minutes. Stronger roasting will generate darker colour and more intense aroma and flavour.
Coffee is typically roasted in horizontal rotating drums that are heated from below or fluidized bed roast chambers where the coffee is heated and moved by hot air. On an industrial scale, the burners are typically heated with gas or oil. Following roasting, the beans are cooled down to room temperature. They may then be packaged as whole beans ready from sale.
If required, the roasted coffee beans may be ground. This is done in a coffee grinder. Grind size needs to be adapted for each intended use (espresso machine, filter brew, instant coffee) as it will also influence the taste in the cup.
Coffee grows in around eighty countries in South and Central America, the Caribbean, Africa and Asia.
Arabica coffee accounts for about three-quarters of coffee cultivated worldwide. It is grown throughout Latin America, Central and East Africa, India and, to some extent, Indonesia.
Robusta coffee is grown in West and Central Africa, throughout South-East Asia and, to some extent. in Brazil.
Brazil is the largest coffee exporting nation, but Vietnam tripled its exports between 1995 and 1999, and became a major producer of Robusta beans. Indonesia is the third-largest exporter and the largest producer of washed Arabica coffee.
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