Coffee Plant

The coffee plant is a woody perennial evergreen dicotyledon that belongs to the Rubiaceae family. Because it grows to a relatively large height, it is more accurately described as a coffee tree. It has a main vertical trunk and primary, secondary, and tertiary horizontal branches. Coffee trees bloom annually with fragrant white flowers that mature into fruits. The word “coffee” also refers to the pit of the plant’s cherry (fruit), which shelters within it the prized coffee bean. The thick and bitter outer skin of the cherry encases the sweet fruit, which is much like a grape. Within the fruit is a slippery thin layer of skin that protects the small, hard bean. A coffee tree matures after about four to five years and then yields about one pound of coffee per year for about 15-20 years. A plant’s coffee berries ripen at various times, requiring pickers to select only the ripest berries and leave the unripe berries for later. Hand picking is preferable, so that unripe berries are not mixed in with the perfectly ripe berries, as occurs with machine picking.

Coffee Plant Varieties

While there are several different coffee species, two main species are cultivated today. Coffea Arabica, known as Arabica coffee, accounts for 70 percent of the world’s production. Coffea Canephora, known as Robusta coffee, accounts for 30 percent and differs from the Arabica coffees in terms of taste. Robusta coffee beans are more robust than the Arabica plants, but produce an inferior tasting beverage with higher caffeine content. Both the Robusta and Arabica coffee plant can grow to heights of 10 meters if not pruned, but producing countries maintain the coffee plant at a height reasonable for easy harvesting.

Coffee Plant Growth and Development

 

Three to four years after the coffee is planted, sweetly smelling flowers grow in clusters in the axils of the coffee leaves. Fruit is produced only in the new tissue. The Coffea Arabica coffee plant is self-pollinating, whereas the Robusta coffee plant depends on cross-pollination. About 6-8 weeks after each coffee flower is fertilized, cell division occurs and the coffee fruit remains as a pin head for a period that is dependent upon the climate. The ovaries then develop into drupes, in a rapid growth period that takes about 15 weeks after flowering. During this time the integument takes on the shape of the final coffee bean. After the rapid growth period the integument and parchment are fully grown and do not increase in size. The endosperm remains small until about 12 weeks after flowering. At this time it will suppress, consume, and replace the integument. The remnants of the integument are what compose up the silver skin. The endosperm will have completely filled the cavity made by the integument nineteen weeks after flowing. The endosperm is now white and moist, but gains dry matter during the next several months. During this time the endosperm attracts more than seventy percent of the total photosynthesizes produced by the tree. The mesocarps expand to form the sweet pulp that surrounds the coffee bean. The coffee cherry changes color from green to red about thirty to thirty five weeks after flowering.

Coffee Plant Root-System

 

The roots of the coffee tree can extend 20-25 km in total length and the absorbing surface of a tree ranges from 400 to 500 m2.There are main vertical roots, tap roots, and lateral roots which grow parallel to the ground. The tap roots extend no further than 30-45 cm below the soil surface. Four to eight axial roots may be encountered which often originate horizontally but point downward. The lateral roots can extend 2 m from the trunk. About 80-90% of the feeder root is in the first 20 cm of soil and is 60-90 cm away from the trunk of the coffee tree. However, the greatest root concentration is in the 30 to 60 cm depth. The root system is strongly affected by the type of soil and the mineral content of the soil. To be thick and strong, coffee roots need an extensive supply of nitrogen, calcium and magnesium. During planting the main vertical roots are often clipped to promote growth of the horizontal roots, which then have better access to water and added nutrients in the top soil.

Coffee Leaves

 

The elliptical leaves of the coffee tree are shiny, dark green, and waxy. The coffee bean leaf area index is between 7 and 8 for a high-yielding coffee. The coffee plant has become a major source of oxygen in much of the world. Each hectare of coffee produces 86 lbs of oxygen per day, which is about half the production of the same area in a rain forest.

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