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One of life’s simple pleasures is really quite complicated For sheer sensory enjoyment, few everyday experiences can Coffee cultivation entails myriad variables that must be moni-
compete with a good cup of coffee. The alluring aroma of tored and regulated. Once a coffee bean is grown, nothing can steaming hot coffee just brewed from freshly roasted be added or removed: the quality must already be present. For beans can drag sleepers from bed and pedestrians into cafés.
a single portion of espresso, 50 to 55 roasted coffee beans are And many millions worldwide would find getting through the required; a single imperfect bean will taint the whole sufficiently day difficult without the jolt of mental clarity imparted by the to be noticeable. This is because human olfaction and taste caffeine in coffee. But underlying this seemingly commonplace senses originated as defense mechanisms that protected our an- beverage is a profound chemical complexity. Without a deep cestors from rotten—hence, unhealthy—foods. Only through understanding of how the vagaries of bean production, roast- modern technology can one economically and consistently ing and preparation minutely affect the hundreds of com- pounds that define coffee’s flavor, aroma and body, a qualitycup would be an infrequent and random occurrence.
Growing Coffee
Connoisseurs agree that the quintessential expression of R A W C O F F E E B E A N S are the seeds of plants belonging to the coffee is espresso: that diminutive heavy china cup half-filled Rubiaceae family, which comprises at least 66 species of the with a dark, opaque brew topped by a velvety thick, reddish- genus Coffea. The two species that are commercially exploit- brown froth called crema. Composed of tiny gas bubbles en- ed are Coffea arabica, which accounts for two thirds of world cased in thin films, the surprisingly persistent crema locks in the production, and C. canephora, often called robusta coffee, with coffee’s distinctive flavors and aromas and much of its heat as one third of global output. Robusta coffee plants and all wild well. Espresso—the word refers to a serving made on request coffee species have 22 chromosomes, whereas arabica has 44.
expressly for the occasion—is brewed by rapidly percolating a Therefore, arabica and other coffee species cannot be crossed small quantity of pressurized, heated water through a com- pressed cake of finely ground roasted coffee. The resulting con- Robusta is a high-yielding and disease-resistant tree stand- centrated liquor contains not only soluble solids but also a di- ing up to 12 meters tall that grows best in warm, humid climes.
verse array of aromatic substances in a dispersed emulsion of It produces a cup featuring substantial body, a relatively harsh, tiny oil droplets, which together give espresso its uniquely rich earthy aroma, and an elevated caffeine content that ranges from 2.4 to 2.8 percent by weight. Although robusta is sold by many Aficionados consider perfectly brewed espresso to be the ul- purveyors, it does not give rise to the highest-quality coffee.
timate in coffee because its special preparation amplifies and Arabica, which originated in the Ethiopian highlands, is a exhibits the inherent characteristics of the beans. Espresso is medium- to low-yielding, rather delicate tree from five to six useful for our purposes as it is in effect a distillation of all the meters tall that requires a temperate climate and considerable numerous techniques by which coffee can be made, including growing care. Commercially grown coffee bushes are pruned the Turkish method and various infusion and filter drip pro- to a height of 1.5 to 2.0 meters. Coffee made from arabica cesses [see box on page 91 for descriptions of alternative cof- beans has an intense, intricate aroma that can be reminiscent of fee-preparation methods]. To know espresso is to know cof- flowers, fruit, honey, chocolate, caramel or toasted bread. Its caffeine content never exceeds 1.5 percent by weight. Because High-quality coffee arises from maintaining close control of its superior quality and taste, arabica sells for a higher price over a multitude of factors in the field, in the plant and in the cup.
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plants to blossom, and some 210 days af-terward red or yellow fruit called cherriesappear. Each cherry contains two oblongseeds—the coffee beans. Because bothflower and fruit can be present simulta-neously on the same branch, the picker’sforefinger and thumb are the best tools togather just the ripe cherries. Stripping en-tire branches by hand or using automat-ed harvesting machines does not discrim-inate between the ripe and the unripecherries.
coffee beans depends on the genetics ofthe plant, the soil in which it grows andthe microclimate, which encompasses fac-tors such as altitude, the amount of rain-fall and sunlight, and daily temperaturefluctuations. Along with the roasting pro-cesses that are applied, these agriculturaland geographical considerations are re-sponsible for the taste differences amongthe many varieties of coffee beans thatsuppliers combine to produce the variousdistinctive blends one can purchase. Processing Coffee
coffee cherries must be processed
immediately after harvest to prevent
spoilage. Producers employ two process-
ing methods: sun-drying and washing.
Effective sun-drying is accomplished by
spreading the cherries out on a patio and
stirring the desiccating fruit frequently to
evenly heat and aerate it. The dried cher-
percent water content of the coffee cher- electric cells detect duds, signaling for eration is accomplished at a speed that no for sorting and bagging. In the alternative one starts with exceptional green beans.
most highly trained eye is incapable of.
pulped, washed, and finally dried and lib- based in Trieste, Italy, use many sophis- ticated process-control techniques to min- thick walls: as much as five to seven mi- R
ERNESTO ILLY is chairman of illycaffè, a beans, including ultraviolet fluorescence dom. During roasting, these 30- to 40-mi- O
analysis to spot moldy beans and trichro- cron-diameter cells serve as tiny reactors matic mapping to generate a color finger- in which all the key heat-driven chemical print (yellow-green, red and infrared) of reactions occur that generate coffee’s se- every day in Italy alone. Illy holds a doc- each lot of beans. At illycaffè, a dichro- ductive taste and fragrance. The cells of THE AUTH
matic sorting system developed in collab- immature beans feature thinner walls.
advanced studies in molecular biology.
Unripe beans also lack the important aro- is applied as a final control right before roasting. As beans fall into bins, photo- the last stages of the ripening process.
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With more than 400 BILLION CUPS consumed every
year, coffee is the world’s most popular beverage Coffee ranks SECOND ONLY TO PETROLEUM in terms
beans, forces all the off-flavors and fra- grances to leave the beans. Sadly, the de- (about $10.4 billion in exports in 2000). Roasting Coffee
ACCORDING TO A SURVEY OF 3,000 AMERICANS CONDUCTED BY
r o a s t i n g is a pyrolytic (heat-driven) THE NATIONAL COFFEE ASSOCIATION IN 2001:
process that greatly increases the chemi- Fifty-two percent of adults (older than 18 years) the roasting, the less desirable the aroma in the U.S. drink coffee every day, representing will be and the stronger the bitterness.
107 MILLION daily drinkers. Another 28 percent of
adults (57 MILLION) drink coffee occasionally.
volatile molecular species, whereas roast- American coffee drinkers consume, on average, ed coffee gives rise to more than 800.
fail to develop fully the welcome aromas, 3.3 (NINE-OUNCE) CUPS OF COFFEE a day.
and acidity tends to come to the fore.
of a roasting machine (basically, a huge, Controversy continues over whether SHADE-GROWN
hot rotating cylinder), residual water in- Smelling Coffee
coffee should be promoted to enhance bird habitats. side each cell is converted to steam, which a r o m a s c i e n c e is highly complex.
Coffee and caffeine have been the subject of extensive scientific study during the past quarter of grances evolved during coffee bean roast- a century, with 1,500 TO 2,000 PAPERS PUBLISHED EVERY
ars, proteins, lipids and minerals within YEAR on the topic. Despite this close scrutiny, few
negative health effects have been definitively linked [see box on next page]. At high heat, from olfactometry, in which skilled testers sniff to the moderate consumption (TWO CUPS A DAY) of
and define the smell of each recognizable caffeinated coffee. In fact, recent work indicates that roasted coffee can be a good source of antioxidants. 1000 B.C. TO A.D. 500 The nomadic Oromos tribe,
ization process called Maillard’s reaction.
composition of each odor. Sniffing roast- living in the kingdom of Kefa (in modern-day ed coffee aromas that have been fraction- Ethiopia), eat coffee, crushed, mixed with fat and shaped into golf ball–size portions, as a pick-me-up. CIRCA 600 Coffee is brought by traders across
the Red Sea into Arabia (modern-day Yemen). the aromas of roses, Darjeeling tea, choco- 12 liters per kilogram of roasted coffee). late, vanilla and violets, as well as truffles, LATE 1400S TO EARLY 1500S Coffee beans, heretofore
an Arabian monopoly, are brought to Turkey, Egypt and Syria by Muslim pilgrims returning from Mecca. called cat scent, which, if diluted, smells Arabian-influenced coffeehouses open in volatile compounds give coffee its famil- Constantinople, Damascus and other Near Eastern cities, where European traders, particularly iar fragrance. Pressure inside each cell in- Venetians, are introduced to the beverage. In the laboratories of illycaffè, techni- CIRCA 1600 Calling it “the bitter invention of Satan,”
cians focus on the strongest odorants.
advisers urge Pope Clement VIII to reject the favorite try to escape but are sealed in by the thick, Imagine listening to a recording of a choir drink of the infidel Ottoman Turks. Instead he decides to give papal authority to coffee, making it oil. Some cells eventually burst, creating 1616 Dutch entrepreneurs start to cultivate coffee
the characteristic popping sound of roast- commercially, beginning with a coffee plant tend to dominate the ensemble. If the vol- obtained from Yemen. By 1658 (according to some
sources, the 1690S), the Dutch are growing coffee in
Ceylon and their East Indian colony of Java. stronger voices will still be recognizable 1714 The mayor of Amsterdam presents the French
even as the choir’s sound fades away. Di- king, Louis XIV, with a coffee plant from Java. 1723 Gabriel Mathieu de Clieu, a French naval officer,
can last from 90 seconds to as long as 40 beyond a certain point, only the strongest carries three coffee seedlings obtained under questionable circumstances from the Royal Botanical Gardens on a perilous voyage to the Caribbean island of Martinique, where one of the plants thrives. ics of the intracellular reactions differ ac- 1727 After having been called to arbitrate a border
cording to roasting time, and so does the dispute between two coffee-growing colonies, final result. A short roasting time, which Dutch Guiana and French Guiana, Francisco de Melo ethylglycolate, which are responsible for Palheta, a Portuguese Brazilian official, smuggles several coffee seedlings to his home estates. 1903 German coffee importer Ludwig Roselius
ruin a cup of coffee by their very presence.
1933 Francesco Illy patents the first
roasting periods, frequently used in poor- characteristic earthy, chemical smell of ro- 1961 Ernesto Valente of Faema, an Italian coffee
machine maker, designs the archetype of the COPYRIGHT 2002 SCIENTIFIC AMERICAN, INC.
Preparing Coffee
Rio taste because it was first discovered in drip coffee than when making espresso.
be found in corked wines as well. Its per- system is shockingly low—six millionths coffee by heated water. The interaction of the four to six minutes of contact with the of a billionth of a gram per milliliter.
boiling water, most of the soluble sub-stances present in the roasted coffee passinto solution. Thus, large quantities ofhighly soluble acids and caffeine dissolve into the cup. In contrast, the much short-er percolation time of espresso allows less acid and only 60 to 70 percent of the caf- CREMA, the dense, reddish-brown foam that tops an espresso, is shown in an enlarged cross dioxide and water vapor bubbles (large circles) surrounded by surfactant films, the crema also and pressurize it to nine atmospheres.
aromatic compounds (particles with red sistency, is placed in a perforated basket borders) and dark fragments of the coffee bean Gas bubble Cumulative Chemical Composition of Espresso with Increasing Extraction Time
grounds adhere to one another thanks toa thin coating of oil, which is as viscous as THE OVEREXTRACTION of espresso (beyond the recommended 30 seconds) leads to the honey. The oil binds the particles togeth- incorporation of undesirable and less soluble aromatic compounds into the drink er into a condensed maze of minuscule air Compound Aroma
that the hydraulic resistance of this bed of coffee grounds must be slightly less than CHOCOLATE
tion water, allowing it to flow through at a rate of around a milliliter a second.
CHOCOLATE
of percolation, a skilled barista (coffee bar CINNAMON
technician) produces about 30 milliliters of dense coffee liquor covered by the all- important crema. If the color of the foam topping is light, it means that the espres- Chemical Concentration (parts per million)
cause the grind was too coarse, the water Extraction Time (seconds)
short. If the crema is very dark in hue andhas a “hole” in the middle, it is likely that Chemical Composition of Raw and Roasted Arabica Coffee
the consistency of the coffee grounds was (percentage of dry matter)
hibits either a white froth with large bub- white spot in the center of the cup if the the coffee grounds, including aroma-filled oil and bits of the cellular structure. The Green Beans
Roasted Beans
(average water content
(average water content
8%–12%)
0%–5%)
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FILTER DRIP METHODS (automatic drip, Melitta, Chemex pots).
the infusion, segregating the grounds at the bottom of the pot.
These popular techniques employ finely ground coffee in Turkish method. Unlike other brewing processes, gentle boiling
receptacles lined with filter paper. A medium grind should be used of the coffee is desirable when using this method. Mix equal with a reusable gold filter. There are two keys to making superior amounts of pulverized coffee, water and sugar in a special pot coffee using these processes: first, rinse the paper filter with called an ibrik, which sits directly over the heat. Stir the mixture as boiling water to remove the papery smell; second, ensure that the it comes to a slow boil. Stop stirring when the powdered coffee no near-boiling-hot brewing water takes no more than four to six longer sticks to a spoon. As the brew just begins to boil and foam minutes to pass through the grounds, thereby producing optimal up, remove the ibrik from the heat. Tap the ibrik to reduce the foam extraction levels. The brewing time of an automatic drip machine somewhat. Repeat the process at least two additional times. The can be controlled by tailoring the quantity of water so that it flows result is a uniquely thick, sweet brew.
for the recommended four to six minutes.
French press or plunger pot. This apparatus steeps the coffee
Adapted from The Great Coffee Book, by Timothy J. Castle and in the hot water before the grounds are filtered out. Combine Joan Nielsen (Ten Speed Press, Berkeley, Calif., 1999). heated water and coarsely ground coffee in the pot and allow it to infuse from two to five minutes, depending on the desiredstrength. Then press the wire-mesh filter/plunger slowly through aromatic volatiles dissolved in the emul- oils, about 0.1 gram a cup. Intact cells in sified oils as long as it remains there. These oily flavor/fragrance carriers mean that the Channel. Please check your local listings.
beverage, along with cell wall fragments, complex chemistry of coffee to enjoy it. SA which endow the foamy crema with whatis called the tiger-skin look.
M O R E T O E X P L O R E
Coffee, Vols. 1–6. R. J. Clarke and R. Macrae. Elsevier Applied Science, 1985.
Coffee: Botany, Biochemistry and Production of Beans and Beverage. M. N. Clifford and
are bound to the dispersed gas bubbles, oil K. C. Willson. Croom Helm, London, 1985.
droplets and solid fragments, all of which Caffeine, Coffee and Health. Edited by S. Garattini. Raven Press, 1993.
are less than five microns in size. The col- Espresso Coffee: The Chemistry of Quality. A. Illy and R. Viani. Academic Press, 1995.
loidal character of the dispersion gives the Coffee: Recent Developments. R. J. Clarke and O. Vitzthum. Blackwell Science, 2001.
International Coffee Organization: www.ico.org
surface tension. Espresso thus visibly coats International Scientific Association of Coffee: www.asic-cafe.org
Coffee industry–supplied information on coffee, caffeine and health: www.coffeescience.org
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