Introduction to Coffee Plant
The exotic coffee plant belongs to the Rubiacee family, Coffea genus, which encompasses various species (about 60). However, only two of them are actually cultivated and marketed: Coffea Arabica and Coffea Canephora, commonly referred to as Robusta. This evergreen plant, which produces flowers and fruit, is a dicotyledon that thrives in hot climates, in the countries between the Tropics of Cancer and Capricorn.
In the wild, it can grow to a height of 3 to 15 meters (10-50 feet) but in order to facilitate the harvest, coffee-growers keep it pruned to a height of less than 3 meters (10 ft). Coffee plantations usually need plenty of water, especially during the phase of full vegetation. For this reason, the size of the harvest is dependent on the climate, and the tropical band seems to ensure the best conditions, as there are no extreme climatic variations in this area.
The fruit is an oval-shaped green drupe that turns bright red or yellow when fully ripe (though some varieties turn deep yellow), thus taking on an appearance similar to wild cherries – hence their name. If it is not harvested at the right time, the cherry starts to ferment and turns dark brown. The branches can hold cherries with different degrees of ripeness due to frequent rainfall, which causes multiple blossoming and fructification.
Close analysis reveals that the cherry is composed of an outer exocarp (skin) and a mesocarp (pulp), which encloses the two seeds or beans. In turn, these are protected by additional membranes: a parchment-like envelope (parchment) and a silvery membrane (silverskin). At times, the cherry can contain a single round berry, likewise split along one side. This is known as a ‘Caracolito’ or peaberry.
The main characteristics of the plant
As already mentioned, climatic conditions and the quality of the soil are extremely important natural factors for growing coffee. The best conditions can be found in the tropical band where the weather is hot and quite humid, abundant rainfall alternates with dry seasons, and the temperature ranges between 15 and 30°C (59 and 86°F). The plant is sensitive to wind, cold, frost and excessive heat. Volcanic soils are the most suitable ones to grow coffee, as they are rich in nitrogen and humus.
Two techniques can be used to grow the new plants: directly from the seed or from cuttings.
- In the first case, the best beans are chosen and are planted in special seedbeds at a depth of approximately 2 cm (0.78 inches). After about 6-8 weeks, slender stalks, bearing a seed on the top, emerge from the ground.
- The second technique consists of cutting the upper part of the branches (tips), which bear 4 leaves. These must be trimmed further in order to produce a twig that is then planted into a seedbed. The first “rootlets” will form after about 1-2 weeks. The plant will gradually sprout leaves and after about a year, when it reaches a height of 30-50 cm (12-20 inches), it will be transplanted to the plantation.
The plants also require care for the first three years, despite the fact that they are not productive yet. They must be watered, supervised with treatments and pruned frequently to prevent illness and poor development.
After so much work, the tree is ready to blossom, and after 7-8 months the ripe cherries can be harvested. Over an average life span of 15-20 years, a plant will produce about 700-800 grams (25-28 oz.) of green coffee a year. Though productivity tends to diminish over the years, through special pruning techniques the plant can become productive again after about 3 years.
Once fertilised, the plant generates a fruit that takes 7-8 months to reach full maturity, depending on both climate and variety. As we have already noted, it is an oval-shaped green drupe which turns bright red or even deep yellow when mature.
On inspection the cherry is made of the following:
- The skin (thin and red)
- The pulp (soft and sweetish)
- The two beans, which are flat on the inside, have a lengthwise groove, and are convex on the outside.
In turn, each bean is protected by two membranes, the parchment and the silverskin. The size of the coffee beans can vary in length from 7 to 15 mm (0.27-0.6″), in width from 6 to 8 mm (0.23-0.3″), and in weight from 0.1 to 0.2 g (0.003-0.007 oz).
Main chemical components
Ever since it was discovered, coffee has been associated with magical effects, medical-therapeutic qualities and stimulant properties. When we drink a cup of coffee, we’re impressed by a wealth of sensory impressions that few other products can match. Much has been written about this topic, but only recently we have gained sufficient knowledge about the chemical substances responsible for these effects.
The most important components of coffee are:
- Caffeine: discovered in the early nineteenth century, it is a member of the alkaloid family and is certainly the best-known component of coffee; caffeine is what makes coffee taste bitter. The percentage varies according to the variety – Arabica or Robusta – and does not undergo significant loss following the roasting process.
- Minerals: the main one is potassium, but there are also small quantities of calcium and magnesium.
- Proteins: roasting partially denatures proteins, which are partially transformed into brown compounds called “melanoidines”.
- Amino acids: due to roasting, they break down, releasing carbon dioxide, and they react to form the aromatic component of the flavour.
- Fat: this category is mainly represented by coffee oils, which are found inside the bean and are mainly made of triglycerides and free fatty acids. In addition, the outermost part of the bean also has a small quantity of wax.
- Carbohydrates: they contribute to forming brown pigments (melanoidine and caramel). They are represented by saccharose (water-soluble) and, mainly, cellulose (not water-soluble). Saccharose in particular, with amino acids, organic acids and trigonelline, contributes to developing the aromas of coffee during the roasting process, forming thousands of volatile substances (aldehydes, ketones, pyrazine, etc.).
- Water: its percentage in green coffee tends to drop to approximately 1% due to evaporation caused by the roasting process.
Composition of coffee (mean data)
|COMPONENTS (mg% /100gr dry substance)||ARABICA||ROBUSTA|
|Caffeine||0.9 – 1.2||1||1.6 – 2.4||2|
|Minerals||3 – 4.2||3.5 – 4.5||4 – 4.5||4.6 – 5|
|Proteins||11 – 13||13 – 15||11 – 13||13 – 15|
|Fats||12 – 18||14.5- 20||9 – 13||11 – 16|
|Oligosaccharides (carbohydrates)||6 – 8||0 – 3.5||5 – 7||0 – 3.5|
|Water||10 – 13||1 – 5||10 – 13||1 – 5|