# Coffee

Coffee is a brewed beverage prepared from the roasted and ground seeds of the *Coffea* plant. Despite being universally called "beans," these seeds are the pits of a small fruit, commonly known as the coffee cherry. Once the cherries are harvested, the seeds are separated from the surrounding pulp, dried, roasted, ground, and finally infused in hot water to produce the dark, aromatic drink consumed across the world. Coffee is valued both as a daily stimulant, owing to its naturally occurring caffeine, and as a sensory product whose flavor reflects its botanical variety, growing region, processing, and roast.

This article surveys the plant and its principal species, the historical spread of coffee cultivation, the major processing and roasting methods, standard brewing practice, and the relationship between roast level and caffeine content.

## The Plant and Its Species

The genus *Coffea* contains many species, but two account for essentially all commercial production. These are *Coffea arabica*, almost always referred to simply as Arabica, and *Coffea canephora*, universally known by its trade name, Robusta.

Arabica is the dominant species in the global market, supplying roughly 60 to 70 percent of world production. It is generally grown at higher altitudes, where cooler temperatures slow the maturation of the cherry and allow more complex sugars and aromatic compounds to develop. The result is a cup that is typically regarded as sweeter, more nuanced, and more layered in flavor, often carrying notes described as floral, fruity, or chocolate-like. Arabica plants are, however, comparatively delicate. They are sensitive to temperature swings, vulnerable to pests, and especially susceptible to coffee leaf rust, a fungal disease that has historically devastated entire growing regions.

Robusta, by contrast, is a hardier plant. It thrives at lower elevations and in warmer, more humid climates that Arabica cannot tolerate. As its name suggests, it is robust: more resistant to disease and pests, more forgiving of difficult growing conditions, and capable of producing a higher yield per plant. These agronomic advantages make it cheaper to cultivate. In the cup, Robusta is generally described as harsher and more bitter, with an earthy or woody character and a heavier body. It contains about twice the caffeine of Arabica, a difference that contributes both to its more aggressive taste and to its natural resistance to insects, since caffeine acts as a chemical deterrent in the plant. Robusta is widely used in instant coffee and in espresso blends, where it lends body and a thick, stable layer of crema.

The table below summarizes the principal contrasts between the two species.

| Trait | Arabica | Robusta |
| --- | --- | --- |
| Share of world production | ~60-70% | remainder |
| Growing altitude | Higher | Lower |
| Hardiness / disease resistance | Lower | Higher |
| Yield | Lower | Higher |
| Caffeine content | Baseline | ~2x that of Arabica |
| Typical flavor | Sweeter, more complex | Harsher, more bitter |

## Origin and Historical Spread

Coffee was first cultivated in the highlands of Ethiopia, where the *Coffea arabica* plant grows wild and where the practice of preparing the seeds as a drink is believed to have originated. From this East African cradle, coffee crossed the Red Sea and took firm root in Yemen, where it was systematically cultivated and traded. The Yemeni port of Mocha became so closely associated with the commodity that its name endures as a coffee term to this day.

Through Yemen and the wider Arab world, coffee spread as both a commercial good and a social institution. Coffeehouses became centers of conversation, commerce, and learning across the region long before the drink was known in Europe. By the 17th century, coffee had reached the European continent, where it was initially regarded as an exotic novelty before rapidly becoming a fixture of urban life. European coffeehouses, like their predecessors in the Arab world, grew into gathering places for merchants, writers, and political thinkers.

As demand grew, colonial powers carried coffee cultivation to tropical regions across the globe, establishing plantations throughout Asia, Africa, and the Americas. This expansion fundamentally reshaped the geography of production. Today the largest producer of coffee in the world is Brazil, whose vast plantations supply an enormous share of the global market. Vietnam ranks second, having risen to prominence largely on the strength of Robusta cultivation. Other significant producers include Colombia, Indonesia, Ethiopia, and several nations of Central America.

## Processing

After harvesting, the coffee cherry must be processed to extract and dry the seed. The processing method has a pronounced effect on the final flavor of the coffee, and three principal approaches are used.

In the **washed** process, also called the wet process, the outer skin and most of the fruit pulp are removed before the seeds are fermented in water to break down the remaining mucilage, then washed clean and dried. Washed coffees tend to present a cleaner, brighter, and more acidic profile in which the intrinsic character of the bean is clearly expressed.

In the **natural** process, also called the dry process, the whole cherry is dried intact in the sun before the seed is extracted. Because the seed remains in contact with the fruit throughout drying, natural coffees often take on heavier body and pronounced fruity, sometimes fermented, sweetness.

The **honey** process, sometimes described as pulped natural, is an intermediate method. The skin is removed but some of the sticky mucilage is deliberately left on the seed during drying. The result generally falls between the washed and natural styles, combining a degree of clarity with added sweetness and body.

## Roasting

Roasting is the application of heat that transforms green coffee seeds into the brown, aromatic beans recognized by consumers. During roasting, the beans undergo extensive chemical changes that develop hundreds of flavor and aroma compounds, drive off moisture, and cause the bean to expand and darken.

Roast levels run along a continuous spectrum from light to dark. Light roasts preserve more of the bean's origin character, often with higher perceived acidity and brighter, more delicate flavors. Medium roasts balance origin character with the sweetness and body developed during roasting. Dark roasts push the process further, producing bolder, more bitter, and sometimes smoky flavors as the original character of the bean gives way to flavors generated by the roast itself. The choice of roast is largely a matter of style and preference, and a single coffee can be roasted to very different effect.

## Brewing

Brewing extracts the soluble compounds of ground coffee into water. The ratio of coffee to water is one of the most important variables in determining strength and balance. A typical brew ratio is about 1:15 to 1:18 by weight, meaning roughly one gram of ground coffee for every 15 to 18 grams of water. A higher proportion of coffee yields a stronger, more concentrated cup, while a higher proportion of water yields a lighter, more diluted one.

Grind size, water temperature, and contact time also shape the result. Finer grinds and longer contact times increase extraction, while coarser grinds and shorter contact times reduce it. Different brewing devices, from drip machines and pour-over cones to French presses and espresso machines, are matched to particular grind sizes and ratios. To compare recipes objectively rather than by taste alone, enthusiasts measure a brew's strength as its TDS and calculate the EY for a given grind and ratio.

## Caffeine

Caffeine is the principal stimulant in coffee and a major reason for its popularity. The amount in a serving depends on the species used, the dose of coffee, and the brewing method. A standard 8-ounce cup of drip coffee contains about 95 mg of caffeine. Espresso is far more concentrated per unit volume, but an individual shot is small, so the caffeine in a single espresso is often comparable to or less than that in a full cup of drip coffee.

A persistent and widespread belief holds that dark roasts contain dramatically more or less caffeine than light roasts. In fact, roast level barely changes the caffeine content of coffee. Caffeine is a remarkably stable molecule that does not break down meaningfully at the temperatures reached during roasting. A dark roast is therefore not decaffeinated by the act of roasting, nor does it carry dramatically less caffeine than a light roast. Measured by weight of coffee, light and dark roasts are nearly equal in caffeine.

The minor differences that people do observe are largely a matter of measurement. Because dark-roasted beans have lost more moisture and expanded more, they are slightly less dense than light-roasted beans. As a result, a scoop measured by volume of dark roast contains marginally fewer beans, while a portion measured by weight contains marginally more, since each bean weighs less. These are small effects of how the coffee is dosed, not of caffeine being destroyed in the roaster. The species used, with Robusta carrying roughly twice the caffeine of Arabica, and the overall dose of coffee relative to water exert a far greater influence on the caffeine in the finished cup than the roast level ever does.

## Summary

Coffee is a brewed drink made from the roasted, ground seeds of the *Coffea* plant. Two species dominate cultivation: Arabica, prized for its sweeter and more complex flavor, and the hardier, higher-caffeine Robusta. From its origins in the Ethiopian highlands, coffee spread through Yemen and the Arab world and reached Europe in the 17th century, eventually becoming one of the most widely traded agricultural commodities, led today in production by Brazil and Vietnam. Processing and roasting choices shape its flavor, while brewing ratio and method shape its strength. And contrary to common assumption, the roast in the cup tells you little about its caffeine, which remains stable through the heat of the roaster.
