The ecological processes behind one of the world’s most popular beverages
You drink it everyday. It’s black. It smells good.
It tastes good too.
A lot of people drink it just like you. They order a “cup of coffee” and drink it quickly before work, or during a break.
Among the millions of people drinking this black fluid, only a few know about the wonderful life of the coffee trees. It’s a story about growing up in luxurious highlands or the slums of the lowlands. It’s the story of finding a good place for a good life.
It is the story of the coffee tree.
The coffee we drink every morning does not come from a single plant. It’s from two different species of plants. Those two species of coffee are like brothers who grew up in different districts of the same city.
Coffea arabica, the Arabian coffee, is originally from the high plateaus of Ethiopia. It grew up at an altitude of 1300–2000m above sea level, where the air is thin and temperatures a little chilly. Plants, pests and insects are less abundant in the tropical highlands that Arabica calls home. In this comfortable environment, Arabica didn’t have to compete against other plants or defend itself against diseases or pests. It grew up with a silver spoon in its mouth, and therefore now it is a rather fragile plant.
Coffea canephora, also known as Robusta, is also from West-Africa but grew up at the lower altitude of 800m. This tree likes warm temperatures between 20–25 C. Growing in the tropical lowlands, Canephora had to make a name for itself, fighting plants and pests to carve out its place in the forest and catch a bit of sunlight. Canephora is more robust; hence its second name Robusta.
The harsher environment and larger area that Robusta originated from contributed to its genetic diversity, as well as to its high caffeine content. Caffeine, the molecule that keeps us awake, is a great weapon against insects and plant-eaters. Robusta beans contain about 2.5% caffeine, whereas Arabica stands at only about 1.5%.
Another important difference between Arabica and Robusta is the way they have sex.
Many plants, as you know, have sex through their flowers. Some flowers have only male parts or only female parts, often on different trees. This means there needs to be both a male tree and a female tree around for them to cross-pollinate.
Arabica is autogamous, meaning that one tree can produce its own seeds simply by making its flowers touch themselves thanks to the wind. On the other hand, a Robusta tree needs another tree to have sex with and create seeds. In this case, the wind is rarely enough, and Robusta needs pollinators to transport its pollens to the flower of another Robusta tree.
This might seem like a disadvantage at first. But thanks to this sex habit, pollens and genetic information gets exchanged more often, so the Robusta species is genetically more diverse than Arabica.
The two species, Arabica and Robusta, represent 99% of the coffee consumed around the world. But there are about seventy other species of Coffea, growing either in their natural habitat or in conservatories. These form a reserve of genetic diversity, which means scientists can mix and match them to create more resistant and flavourful coffee plants.
Though they’re different, the species of coffee have a lot in common. A young coffee plant starts to produce the beloved coffee beans in its second year. It reaches its normal production at the age of five, and can stay productive for thirty years.
In nature, where nobody expects them to produce fruits, a coffee tree can live in retirement right up to the ripe old age of eighty.
Once adult, Robusta is about five metres tall, while Arabica stands at about three. Their roots branch out in all directions and can go upto three metres deep. But most of them stay near the surface, in the first 30 centimetres of dirt, to catch the water from fresh rains. Only 10% of the roots burrow deeper; Arabica roots usually go deeper than Robusta ones.
Robusta trees bear twice as many flowers as Arabica, which means they can provide twice as many fruits. Flowering happens after the dry season and is often triggered by a large rainfall. The drier the year, the more intense the flowering because the plant is scared by the lack of water and wants to have many seedlings in case it dies.
Not all flowers turn into fruit. If conditions are too wet or too hot, some flowers get damaged and fruit production goes down. What’s more, the flowers take a long time to mature into fruit. It’s only after several months (6–9 for Arabica and 9–11 for Robusta) that flowers will produce the very expected fruits.
An Arabica tree can produce about 5 kg of fruits while Robusta can produce about 10 kg. But that doesn’t mean you’ll get 5 or 10 kilos of coffee beans! The fruits go through a long round of processing, so the weight of the final coffee beans will be only about 20% that of fresh coffee cherries.
One nice thing about coffee is that it doesn’t have to be grown on flat ground. You can even establish your plantation on a steep slope — if you take the necessary precautions.
Coffee is grown in many tropical countries in Latin America, Africa and Asia, where the weather is warm and humid as the coffee loves it. As mentioned earlier, Arabica prefers highlands while Robusta settles well in the low.
While the coffee itself will grow happily on slopes, soil erosion must be controlled. The soil can’t be too shallow, as it has to accommodate the three-metre-long roots of adult trees. But you can’t just press it down to make it stay: a compact soil rich in clay won’t allow water to filter through, which means it could create water stress in the plant population.
One solution is to make flat terraces, combined into a “giant’s staircase” of sorts. Or you could plant ‘cover crops’ which fill the gaps in the coffee, making sure all the soil is protected from the splash of the raindrops.
Water and temperature are the two most important environmental factors to predict the health and production of the coffee plantation. In regions where frost can occur, like the north of Vietnam and some parts of China and Brazil, it is vital to plant coffees on hills and avoid valleys. Cold air usually accumulates in these areas, because of the depression, and coffee plants can’t survive temperature below zero degrees Celsius — they’ll freeze to death!
Being a tropical plant, coffees are adapted to high temperatures rather than low — but too much heat can still hinder their health.
One way to regulate temperature is to intercrop coffee with shade trees. Natural and autonomous air-conditioners, the trees can prevent coffee from overheating. They also maintain a certain humidity under their canopy, and can pump up water from deeper layers of the soil to make it accessible to coffee trees.
Shade trees do more than stabilise the temperature: they also protect coffee against the wind and extreme weather. What’s more, they produce valuable goods like timber, fruit or fodder, which can be used by humans in addition to coffee. Those shade trees are especially useful in extreme conditions, where coffee trees would struggle to grow either because of high temperature or lack of water.
Agroforestry systems, which use shade trees rather than just coffee, can maintain more biodiversity and store more carbon than coffee monoculture. That’s why it’s beneficial to encourage farmers to plant shade trees. They’re a promising tool to reduce the effect of climate change and mitigate climate change.
Coffee is the second-most traded agricultural product in the world, after natural oil. A large area in tropical countries is dedicated to grow this luxurious crop, which is mostly consumed in the northern countries.
If you’re a coffee aficionado, you can learn more about the coffee bean and improve your own experience. There is so much to know about coffee: biology, growing and roasting methods, flavours, brewing etc. Coffee is such a complex drink that you could spend a life learning about it.
But you can start right now!
Looking for references? A lot of the information in this article is taken from the following book: Jean Nicolas Wintgens — Coffee Growing, Processing, Sustainable Production — A Guidebook for Growers, Processors, Traders, and Researchers (2004)