A coffee tree is an evergreen that takes roughly three to four years from planting to its first real crop. In most growing regions flowering is triggered by rain after a dry spell: buds that have been waiting open together into white, jasmine-scented blossom that lasts only a few days. Each flower can become a cherry.
The fruit then takes many months to mature — around nine for arabica, longer for robusta. Where there is one clear wet season there is one main harvest a year. Near the equator, where rain is spread across the year, trees can carry flowers, green fruit and ripe fruit at the same moment, giving two harvests or an almost continuous one.
That overlap is the central difficulty of harvesting. Cherries on the same branch ripen at different times, and only ripe fruit has the sugars and developed seed that make good coffee. Picking only the ripe ones means returning to the same tree several times by hand. Stripping a branch in one pass, or harvesting by machine, is far cheaper and mixes ripe with unripe, which then has to be sorted out afterwards.
Coffee grows in a band around the tropics. Arabica is a plant of cool tropical highlands and is damaged by both frost and sustained heat, which is why, near the equator, it is grown high up. Further from the equator the same temperatures are found lower down, so 'high altitude' means different numbers in Colombia and in Brazil.
What altitude really supplies is cooler temperature. Cooler conditions slow the ripening of the fruit, and slower ripening is widely associated with denser seeds and more acidity and aromatic complexity. This is a strong tendency and the basis of grading by altitude in several Central American countries. It is not a guarantee: variety, farming and processing can outweigh it, and excellent coffees are grown at modest elevations.
Soil and shade matter in less tidy ways. Coffee is grown on volcanic soils in many famous regions, but also on others; what it needs is good drainage and nutrition. Traditional farms grow coffee under shade trees, which moderate temperature and support biodiversity at some cost to yield, while full-sun systems yield more and demand more inputs.
Three problems have shaped coffee farming more than any others. Coffee leaf rust is a fungus that attacks the leaves and can strip a tree, cutting yield for seasons afterwards; it destroyed coffee growing in Sri Lanka in the nineteenth century and caused severe losses in Central America in the 2010s. Coffee berry disease is another fungus, affecting the fruit, and is a serious problem in parts of Africa. The coffee berry borer is a small beetle that bores into the cherry and lays its eggs in the seed.
Farmers respond with resistant varieties, with fungicides and traps, with shade and pruning, and by moving uphill. Resistance has usually come from crossing arabica with robusta-derived material, which historically came with a reputation for lower cup quality — a tension that Level 3 returns to.
Arabica is especially exposed to climate change. It has a narrow comfortable temperature range and very little genetic diversity to adapt with. Research has projected substantial losses in the area suitable for arabica by mid-century under continued warming, with suitable land shifting to higher elevations that are limited in extent and often forested. This is one reason for current interest in other coffee species.
Your task. Use the top-producers chart and the origin pages to find three countries that grow mainly arabica and three that grow mainly robusta. For each, note roughly how far it is from the equator and how high its coffee is grown.
What to notice. The arabica origins cluster in highlands; the large robusta origins are lower and hotter. Brazil is the instructive exception: arabica at moderate altitude, far enough from the equator to be cool.
Exercise: Sorting a handful of beans
Objective. See, in roasted coffee, evidence of what happened to the fruit on the tree.
You will need
About 50 g of whole roasted beans, a white plate, good light
Optionally a second, cheaper coffee to compare
Keep the same
Sort the same weight of each coffee if comparing two
Procedure
Spread the beans in a single layer.
Pick out any that are clearly paler than the rest, any that are broken, and any shell-shaped or hollow pieces.
Count each group.
Look at a normal bean: find the centre cut and any papery chaff left in it.
If you have enough pale beans, crush one and smell it beside a normal bean.
What to notice
How uniform are size and colour?
How many pale beans are there in the sample?
Do the pale beans smell different?
Reading what you found
Pale beans that did not brown with the rest are usually called quakers and are generally attributed to unripe fruit, which lacks the sugars that brown during roasting. Their number tells you something about how selectively the cherries were picked and sorted. Uniform size points to screening at the mill. None of this tells you how the coffee tastes — only how carefully it was handled.
What this cannot show
Roasted beans show only some defects. Formal grading is done on green coffee, against a written defect standard.
A light roast makes pale beans harder to spot; a dark roast hides them almost entirely.
A protocol for you to run. CoffeeHQ has not run it and reports no result from it.
Two coffees sit side by side in a shop. One is labelled 1,900 metres, the other 1,200 metres, and the first costs more. A customer assumes the higher one must taste better.
Reasoning it out
Altitude matters because of temperature, and temperature depends on latitude as well.
1,200 metres far from the equator can be as cool as 1,900 metres on it.
Altitude says nothing about variety, how selectively the fruit was picked, or how it was processed and roasted.
So the number is one input into a likely style — denser, brighter — rather than a ranking.
What to do
Read the altitude with the country. Then look for the things it does not tell you: variety, processing and roast date. If the customer prefers low-acid, heavy coffee, the lower-grown one may well be the better buy for them.
Check yourself
Answer in your head first. Nothing is scored and nothing you open here is recorded.
1. Why does good coffee have to be picked by hand, several times?
Show the answer
Cherries on the same branch ripen at different times, and only ripe ones make good coffee.
Selective picking means repeat passes, which is labour — and a large part of what quality costs.
World Coffee Research variety and agronomy resources — World Coffee Research (WCR)
Royal Botanic Gardens, Kew — peer-reviewed research on Coffea species — Royal Botanic Gardens, Kew (A. P. Davis and colleagues)
Food and Agriculture Organization coffee and agricultural data — Food and Agriculture Organization of the United Nations (FAO)
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