Coffee

Nathan Myhrvold for Britannica on the history of the coffee beverage. Our Big Island Circle Tour visits the Premium Kona Coffee Farm where you can sample the delicious Kona coffee.

coffee, beverage brewed from the roasted and ground seeds of the tropical evergreen coffee plants of African origin. Coffee is one of the three most popular beverages in the world (alongside water and tea) and one of the most profitable international commodities. Though coffee is the basis for an endless array of beverages, its popularity is mainly attributed to its invigorating effect, which is produced by caffeine, an alkaloid present in coffee.

Two species of coffee plants, Coffea arabica and C. canephora, supply almost all of the world’s consumption. Arabica is considered a milder and more flavourful and aromatic brew than Robusta, the main variety of C. canephora. The flatter and more elongated Arabica bean is more widespread than Robusta but more delicate and vulnerable to pests, requiring a cool subtropical climate; Arabica must grow at higher elevations (2,000–6,500 feet [600–2,000 metres]), it needs a lot of moisture, and it has fairly specific shade requirements. Latin America, eastern Africa, Asia, and Arabia are leading producers of Arabica coffee. The rounder, more convex Robusta bean, as its name suggests, is hardier and can grow at lower altitudes (from sea level to 2,000 feet). Robusta coffee is cheaper to produce, has twice the caffeine content of Arabica, and is typically the bean of choice for inexpensive commercial coffee brands. Western and Central Africa, Southeast Asia, and Brazil are major producers of Robusta coffee.

History

Wild coffee plants, probably from Kefa (Kaffa), Ethiopia, were taken to southern Arabia and placed under cultivation in the 15th century. One of many legends about the discovery of coffee is that of Kaldi, an Arab goatherd who was puzzled by the strange antics of his flock. About 850 CE Kaldi supposedly sampled the berries of the evergreen bush on which the goats were feeding and, on experiencing a sense of exhilaration, proclaimed his discovery to the world.

Whatever the actual origin of coffee, its stimulating effect undoubtedly made it popular. Ironically, though Islamic authorities pronounced the drink intoxicating and therefore prohibited by the Qurʾān, many Muslims were attracted to the beverage as a substitute for alcohol, also prohibited by the Qurʾān. Despite the threat of severe penalties, coffee drinking spread rapidly among Arabs and their neighbours and even gave rise to a new social and cultural entity, the coffeehouse.

Coffee was introduced into one European country after another throughout the 16th and 17th centuries. Many accounts are recorded of its prohibition or approval as a religious, political, and medical potion. By the end of the 17th century, coffeehouses were flourishing across Britain, the British colonies in America, and continental Europe.

Until the close of the 17th century, the world’s limited supply of coffee was obtained almost entirely from the province of Yemen in southern Arabia. But, with the increasing popularity of the beverage, propagation of the plant spread rapidly to Java and other islands of the Indonesian archipelago in the 17th century and to the Americas in the 18th century. Coffee cultivation was started in the Hawaiian Islands in 1825.

By the 20th century the greatest concentration of production was centred in the Western Hemisphere—particularly Brazil. In the late 19th and early 20th centuries, industrial roasting and grinding machines came into use, vacuum-sealed containers were invented for ground roasts, and decaffeination methods for green coffee beans were developed. After 1950 the production of instant coffee was perfected, which led to increased production of the cheaper Robusta beans in Africa.

Processing the bean

The ripened fruits of the coffee plant are known as coffee cherries, and each cherry generally contains two coffee seeds (“beans”) positioned flat against one another. About 5 percent of the cherries contain only one seed; called peaberries, those single seeds are smaller and denser and produce, in the opinion of some, a sweeter, more flavourful coffee.

The cherries are processed by disengaging the coffee seeds from their coverings and from the pulp and by drying the seeds; all beans must be removed from their fruit and dried before roasting. Three techniques are used for processing the coffee: the dry, or “natural,” process, the wet (and washed) process, and a hybrid process called the semi-washed, or “pulped natural,” method. The coffee resulting from those processes is called green coffee, which is then ready for roasting. 

Grading

After green coffee has been hulled and processed, it is ready to be graded and sold for roasting. The practice of grading and classifying coffee gives sellers and buyers a guarantee concerning the origin, nature, and quality of the product to aid their negotiations. Each coffee-producing country has a certain number of defined types and grades—based on characteristics such as growing altitude and region, botanical variety, method of processing, roast appearance, and bean size, density, and defects—but there is no universal grading and classification system. Some coffee is shade-grown and is more likely to be certified organic. Fair Trade coffee, part of the larger Fair Trade movement, arose to ensure that coffee is harvested and processed without child labour and dangerous herbicides and pesticides and that growers and exporters, particularly in the poorer regions of the coffee-growing world, are paid a fair price. How well such Fair Trade standards are enforced is a matter of controversy. The Rainforest Alliance certification and the Smithsonian Institution’s Bird Friendly certification are awarded to sustainable shade-grown coffee that protects biodiversity.

Decaffination

The term decaffeinated coffee may strike some as an oxymoron, but a number of coffee drinkers relish the taste of coffee but cannot tolerate the jolt from caffeine. The main methods of decaffeination are based on chemical solvents, carbon filtering, carbon dioxide extraction, or triglycerides. In all cases, to make “decaf,” the caffeine is removed in the green bean stage, before the coffee is roasted. Regardless of the method of decaffeination, some adulteration of the coffee bean results along the way, and in no case is 100 percent of the caffeine removed. Extracting a good shot of espresso from decaf coffee beans is perhaps the biggest challenge of all.

Roasting

The aromatic and gustatory qualities of coffee are developed by the high temperatures to which they are subjected during roasting or broiling. Temperatures are raised progressively from about 180 to 250 °C (356 to 482 °F) and heated for anywhere from 7 to 20 minutes, depending on the type of light or dark roast desired. The most important effect of roasting is the appearance of the characteristic aroma of coffee, which arises from very complex chemical transformations within the bean. Roasting too long can destroy volatile flavour and aroma compounds, and Robusta beans are often deliberately overroasted (as in the dark French and Italian roasts) to rid the coffee of its natural harshness. 

Grinding

Some coffees are left as whole beans to be ground at the time of purchase or by the consumer at home. Much coffee, however, is ground, or milled, by the manufacturer immediately after roasting. In most modern roasting plants, grinding is accomplished by feeding the coffee through a series of serrated or scored rollers, set at progressively smaller gaps, that first crack the beans and then cut them to the desired particle size.

The degree of fineness is important. If a coffee is too coarse, water filters through too fast to pick up flavour; if it is too fine, water filters through too slowly and retains particles that deposit at the bottom of the cup.

Packaging

Effective packaging prevents air and moisture from reaching the coffee. Ground coffee alters rapidly and loses its aromatic qualities within a few days if it is not put into hermetically sealed containers immediately.

The air, especially in humid atmospheres, causes rancidity through the oxidation of fatty components. Modern packaging materials, plastic films such as polyethylene and complexes of aluminum and cellulose, are capable of conserving the quality of coffee for a time. The most satisfactory solution to the problem, however, is packing under vacuum or in an inert gas, in rigorously impervious containers.

At the turn of the 21st century, manufacturers responded to consumer desire for freshness and easy-to-brew systems by producing single-cup coffeemakers using coffee capsules—small disposable containers filled with a premeasured amount of coffee and sealed airtight to maintain freshness. Their ease of use made them very popular, though they have been criticized for the plastic waste they generate.

Using coffee

Brewing and drinking

There are both hot and cold methods of extracting flavour and aroma from ground coffee, and the caffeine content varies with the variety of bean and method of brewing. Generally speaking, one serving (five fluid ounces) of Arabica instant coffee contains about 70 mg of caffeine, while a serving of brewed Robusta may contain 200 mg.

In steeping or boiling, pulverized coffee is measured into hot water, which is usually then boiled before being poured off the grounds. In percolation, water is brought to a boil in an urn and fed up a tube to a basket holding the coffee. After filtering through the coffee, the water drips back to the urn, where it is forced back up the tube and recirculated until the brew has reached the desired strength. In the filter, or drip, method, hot water is slowly filtered through the coffee and dripped into a receptacle; it is not recirculated.

The espresso machine forces boiled water under pressure through finely ground coffee. Single-serve coffeemakers also force hot water through coffee grounds.

A French press, however, uses infusion to make the coffee. After the coffee has steeped in the hot water, a mesh-lined plunger is used to push the grounds to the bottom, leaving the coffee above ready to pour directly from the container. Many traditionalists consider French-press coffee second only to the rich flavour of espresso.

In vacuum brewing, steam pressure pushes heated water into an upper chamber, which holds the grounds. Once removed from the heat, steam recondenses in the lower chamber, thus creating a partial vacuum. With the pressure now higher in the upper chamber, the brewed coffee is forced back down through the filter-topped spout into the lower chamber, where it is ready to drink.

There is a long-standing tradition that the best way to serve coffee drinks is “fresh and hot,” within moments of being brewed, though that is not necessarily the case. It is true that espresso should be enjoyed immediately, before the highly volatile aromas dissipate, but brewed coffee that is too hot not only can burn the tongue but also masks the full complement of flavours. Only after it has cooled slightly can more of the inherent flavour be captured. In fact, professional coffee tasters typically wait five or six minutes before tasting a brew. A more moderate temperature produces a more authentic flavour profile. Because of those effects, the temperature of water used for brewing should be calibrated to remain consistent from one brewing cycle to the next.

Finally, high temperature is not needed to brew coffee—as long as one is willing to wait about 12 hours. In cold-water extraction, dampened grounds are left to sit and steep. When strained after some 12 hours, the resulting “cold brew” has a robust but smooth taste without the bitter acids and oils that traditionally accompany hot-water extraction methods. The cold concentrate keeps well for up to two weeks when refrigerated, and it is ideal as a cooking ingredient, as when making coffee ice cream.

Instant Coffee

In the manufacture of instant coffee (called soluble coffee in the industry), a liquid concentration of coffee prepared with hot water is dehydrated. This can be done by spray-drying (by drying with a hot gas) or by freeze-drying (a dehydration process known as lyophilization). The operations are complex, and methods vary among manufacturers. The resulting soluble powder, on the addition of hot water, forms reconstituted coffee. The average yield is 25 to 30 percent by weight of the ground coffee, thereby lowering shipping costs. Instant coffee is obviously quicker to make than brewed coffee, and it enjoys a longer shelf life than coffee beans, but it picks up moisture readily and must be kept dry. The taste of instant coffee is also widely considered inferior to brewed coffee.

Cooking with coffee

Water is not the only vehicle for conveying coffee’s character once it has left the bean. Coffee can also be made in alcohol or oil. Although coffee made that way is not good for drinking, it has interesting culinary applications.

Coffee extracted into alcohol, for example, makes a useful ingredient for crafting cocktails. It can also be a good way to add a small amount of coffee aroma to a sauce without adding bitterness. Most of the bitter compounds are not extracted if pure ethanol (such as Everclear) is used. The resulting concentrate is analogous to vanilla extract.

Coffee made with a mixture of water and alcohol can produce a bit (if not the best) of both worlds: the pure, smooth character that alcohol attracts plus the extra taste compounds that water draws from the coffee. Vodka, a pure neutral spirit diluted with water, is a great candidate for that approach.

If one uses a pure fat, such as a neutral cooking oil or clarified butter, to make coffee, only the fat-soluble aroma compounds in the beans will be captured. That does include most of the aromas, but it carries none of the compounds that contribute to taste. In certain cases, that may be the desired effect. There too a greater balance can be achieved by adding some water to the mix. Melted unclarified butter or heavy cream both contain plenty of water, for example. Cream infused with freshly crushed coffee beans produces an intensely flavoured ice cream.

Because espresso is extracted at higher pressure than coffee brewed other ways, the compounds drawn off the beans are more volatile and dissipate quickly, which is why espresso should be consumed immediately. By the time espresso is integrated into a dish and the cooking or preparation of the latter is complete, the peak flavour of the coffee has been lost.

Health effects

Coffee consumption has been associated with various health benefits and health risks. In general, moderate consumption, amounting to three or four cups daily, is linked to a reduced risk of cardiovascular disease, type 2 diabetes mellitus, liver cancer, and Parkinson disease. Research has also linked moderate coffee consumption to a longer life span.

Excessive coffee consumption can cause sleep disturbances, anxiety, jittery sensations, and heartburn. Studies conducted in the 20th century suggested a causative link between coffee and cancer. In 2016, however, the World Health Organization (WHO) removed coffee from the list of possible carcinogens because multiple studies had debunked a possible causative association between coffee consumption and cancer.