One of life’s simple pleasures is really quite complicated The compleCoffeexity of

By Ernesto Illy Photographs by Tina West

or 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 Fsteaming 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- identify 50 nearly perfect beans. pounds that define coffee’s flavor, aroma and body, a quality cup would be an infrequent and random occurrence. Growing Coffee Connoisseurs agree that the quintessential expression of RAW COFFEE BEANS 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- to produce a hybrid plant. 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 taste, smell and “mouthfeel.” 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 fee in all its forms. 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. than its hardy, rougher cousin.

86 SCIENTIFIC AMERICAN JUNE 2002 COPYRIGHT 2002 SCIENTIFIC AMERICAN, INC. COPYRIGHT 2002 SCIENTIFIC AMERICAN, INC. A good rainfall induces arabica coffee plants to blossom, and some 210 days af- terward red or yellow fruit called cherries appear. Each cherry contains two oblong seeds—the coffee beans. Because both flower and fruit can be present simulta- neously on the same branch, the picker’s forefinger and thumb are the best tools to gather 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 unripe cherries. The ultimate quality of the resulting coffee beans depends on the genetics of the plant, the soil in which it grows and the microclimate, which encompasses fac- tors such as altitude, the amount of rain- fall and sunlight, and daily temperature fluctuations. Along with the roasting pro- cesses that are applied, these agricultural and geographical considerations are re- sponsible for the taste differences among the many varieties of coffee beans that suppliers combine to produce the various distinctive 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 ries are run through a machine that ry is reduced to the 10 to 12 percent them to be rejected individually with a crushes the hulls and then removes both moisture level of a prime raw, or green, puff from an air nozzle. The sorting op- the hulls and the surrounding parchment coffee bean. eration is accomplished at a speed that no membrane layer, thus freeing the beans One of the greatest challenges in pro- human hand can match (400 beans a sec- for sorting and bagging. In the alternative ducing superior coffee is ensuring that ond) and with a precision that even the approach, the fruit is mechanically one starts with exceptional green beans. most highly trained eye is incapable of. pulped, washed, and finally dried and lib- Premium producers, such as illycaffè, A perfect mature green coffee bean is erated from the parchment covering. The based in Trieste, Italy, use many sophis- composed of cells with uncommonly goal of either route is the same: the 65 ticated process-control techniques to min- thick walls: as much as five to seven mi- imize the percentage of defective coffee crons, an exception in the vegetal king- ERNESTO ILLY is chairman of illycaffè, a beans, including ultraviolet fluorescence dom. During roasting, these 30- to 40-mi- family business based in Trieste, Italy, analysis to spot moldy beans and trichro- cron-diameter cells serve as tiny reactors that his father founded in 1933. Over matic mapping to generate a color finger- in which all the key heat-driven chemical two million illy espressos are served 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 AUTHOR torate in chemistry and has completed matic sorting system developed in collab- immature beans feature thinner walls. advanced studies in molecular biology. oration with the English company Sortex Unripe beans also lack the important aro- His goal is to harness science to create is applied as a final control right before matic precursor proteins that develop in the truly perfect cup of espresso. roasting. As beans fall into bins, photo- the last stages of the ripening process.

88 SCIENTIFIC AMERICAN JUNE 2002 COPYRIGHT 2002 SCIENTIFIC AMERICAN, INC. With more than 400 BILLION CUPS consumed every year, coffee is the world’s most popular beverage (besides water, of course). Fermented beans are composed of cells er countries in which many consumers ✹ that have been emptied of these crucial can afford only low-priced, defective Coffee ranks SECOND ONLY TO PETROLEUM in terms constituents by molds or bacteria. beans, forces all the off-flavors and fra- of dollars traded worldwide (about $10.4 billion in exports in 2000). grances to leave the beans. Sadly, the de- ✹ sirable tastes and aromas flee as well, Roasting Coffee ACCORDING TO A SURVEY OF 3,000 AMERICANS CONDUCTED BY roasting is a pyrolytic (heat-driven) yielding a rather bitter cup. THE NATIONAL COFFEE ASSOCIATION IN 2001: process that greatly increases the chemi- The higher the final temperature of Fifty-two percent of adults (older than 18 years) cal complexity of coffee. The aroma of the roasting, the less desirable the aroma in the U.S. drink coffee every day, representing green coffee contains some 250 different 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- Conversely, low roasting temperatures 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. When subjected to the staged heating 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 aroma science is highly complex. Coffee and caffeine have been the subject of promotes diverse, complicated chemical Researchers typically analyze the fra- extensive scientific study during the past quarter of reactions among the cornucopia of sug- grances evolved during coffee bean roast- a century, with 1,500 TO 2,000 PAPERS PUBLISHED EVERY ars, proteins, lipids and minerals within ing by gas chromatography coupled with 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 185 to 240 degrees Celsius, sugars com- and define the smell of each recognizable caffeinated coffee. In fact, recent work indicates that bine with amino acids, peptides and pro- element. Mass spectrometry is frequent- roasted coffee can be a good source of antioxidants. ✹ teins according to a well-known caramel- ly then applied to identify the chemical 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 The end products are brownish, bitter- ed coffee aromas that have been fraction- Ethiopia), eat coffee, crushed, mixed with fat and sweet glycosylamine and melanoidins— ated by a gas chromatograph is an en- shaped into golf ball–size portions, as a pick-me-up. which give rise to coffee’s dominant lightening experience: one may recognize CIRCA 600 Coffee is brought by traders across the Red Sea into Arabia (modern-day Yemen). taste—along with carbon dioxide (up to the aromas of roses, Darjeeling tea, choco- 12 liters per kilogram of roasted coffee). late, vanilla and violets, as well as truffles, LATE 1400STOEARLY 1500S Coffee beans, heretofore an Arabian monopoly, are brought to Turkey, Egypt Simultaneously, a wide variety of low- soup, cheese, sweat and even what is and Syria by Muslim pilgrims returning from Mecca. er-mass aromatic molecules emerge; these called cat scent, which, if diluted, smells Arabian-influenced coffeehouses open in volatile compounds give coffee its famil- like sauvignon blanc wine but in a con- Constantinople, Damascus and other Near Eastern cities, where European traders, particularly iar fragrance. Pressure inside each cell in- centrated sample is disgusting. Venetians, are introduced to the beverage. creases to as much as 20 to 25 atmo- In the laboratories of illycaffè, techni- CIRCA 1600 Calling it “the bitter invention of Satan,” spheres as the steam and carbon dioxide 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 low-porosity cell walls and a coating of of 800 singers that includes the strong acceptable for Roman Catholics. oil. Some cells eventually burst, creating solo voices of Jessye Norman, Luciano 1616 Dutch entrepreneurs start to cultivate coffee the characteristic popping sound of roast- Pavarotti and several other virtuosi who commercially, beginning with a coffee plant ing coffee. During roasting, coffee bean 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 volume increases by half or more; bean ume of the playback is reduced, the Ceylon and their East Indian colony of Java. mass decreases by a fifth. stronger voices will still be recognizable 1714 The mayor of Amsterdam presents the French Depending on the temperatures and even as the choir’s sound fades away. Di- king, Louis XIV, with a coffee plant from Java. procedures applied, the roasting process luting the aroma of coffee is analogous; 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 minutes. Twelve minutes, however, is the compounds are perceived. Unfortunately, questionable circumstances from the Royal Botanical Gardens on a perilous voyage to the Caribbean traditional duration. The thermodynam- the most powerful molecules in the smell island of Martinique, where one of the plants thrives. ics of the intracellular reactions differ ac- of a coffee sample are those originating 1727 After having been called to arbitrate a border cording to roasting time, and so does the from defective beans. dispute between two coffee-growing colonies, final result. A short roasting time, which Molecules such as ethylbutanoate and Dutch Guiana and French Guiana, Francisco de Melo Palheta, a Portuguese Brazilian official, smuggles requires a great deal of thermal energy, ethylglycolate, which are responsible for several coffee seedlings to his home estates. minimizes weight loss but imparts to the the unpleasant aroma of immature beans, 1903 German coffee importer Ludwig Roselius cup a metallic bitterness stemming from ruin a cup of coffee by their very presence. perfects decaffeinated coffee. the presence of polyphenols that do not Likewise, methylisoborneol and trichlor- 1933 Francesco Illy patents the first have enough time to react properly. Long oanisole (TCA) molecules produce the automatic espresso machine. 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 modern espresso machine. www.sciam.com COPYRIGHT 2002 SCIENTIFIC AMERICAN, INC. busta coffees. TCA, which is also called Preparing Coffee er, subtly different when making common Rio taste because it was first discovered in the next major step in the trans- drip coffee than when making espresso. coffees grown around Rio de Janeiro, can formation of roasted beans into a cup of When filter drip coffee is prepared, hot be found in corked wines as well. Its per- espresso is the extraction of the active water passes through a loose aggregation ception threshold to the human olfactory components in the roasted and ground of medium-size coffee grounds. During 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. hot water and coffee grounds is, howev- boiling water, most of the soluble sub- stances present in the roasted coffee pass into solution. Thus, large quantities of highly soluble acids and caffeine dissolve THE CHEMISTRY into the cup. In contrast, the much short- OF COFFEE er percolation time of espresso allows less acid and only 60 to 70 percent of the caf- CREMA, the dense, reddish-brown foam that feine to dissolve into the brew. tops an espresso, is shown in an enlarged cross Brewing espresso requires specialized section. Composed mainly of tiny carbon equipment that can heat water to a tem- dioxide and water vapor bubbles (large circles) perature of between 92 and 94 degrees C surrounded by surfactant films, the crema also and pressurize it to nine atmospheres. includes emulsified oils containing key Coffee, ground to a fine to medium con- aromatic compounds (particles with red borders) and dark fragments of the coffee bean sistency, is placed in a perforated basket cell structure. Gas bubble Oil particles and firmly tamped down to create a com- pacted bed of particles. The compressed Cumulative Chemical Composition of Espresso with Increasing Extraction Time grounds adhere to one another thanks to THE OVEREXTRACTION of espresso (beyond the recommended 30 seconds) leads to the a thin coating of oil, which is as viscous as incorporation of undesirable and less soluble aromatic compounds into the drink honey. The oil binds the particles togeth- (printed in red). er into a condensed maze of minuscule air Compound Aroma OPTIMAL passages. Experimentation has shown 3 2,4-decadienal RANCID that the hydraulic resistance of this bed of UNDEREXTRACTION OVEREXTRACTION ethylgujacol SMOKE coffee grounds must be slightly less than 2.5 2-ethyl-3,5- the pressure of the steaming-hot extrac- dimethylpyrazine CHOCOLATE tion water, allowing it to flow through at 2 2-ethyl-3,6- a rate of around a milliliter a second. dimethylpyrazine CHOCOLATE Using the recommended 30 seconds 1.5 2,4-nonadienal RANCID of percolation, a skilled barista (coffee bar methylsalicilate CINNAMON technician) produces about 30 milliliters b-damascenone TEA 1 of dense coffee liquor covered by the all- DMTS SULFUR important crema. If the color of the foam isovaleraldehyde SWEET 0.5 topping is light, it means that the espres- a-ionone FLOWERS so has been underextracted, probably be-

Chemical Concentration (parts per million) linalool FLOWERS 0 cause the grind was too coarse, the water 10 20 30 40 50 60 temperature too low or the time too Extraction Time (seconds) short. If the crema is very dark in hue and

has 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) too fine or the quantity of grounds was Caffeine

too large. An overextracted espresso ex- illustrations Trigonelline hibits either a white froth with large bub- Proteins and Amino Acids bles if the water was too hot or just a Sugars (mostly white spot in the center of the cup if the

polysaccharides) brewing time was too long. ); NINA FINKEL ( Acids The percolation process also washes Lipids out components present on the surface of micrograph Carmelization and the coffee grounds, including aroma-filled Condensation Products oil and bits of the cellular structure. The Green Beans Roasted Beans Volatile Aromas

high pressure generated by the espresso ILLYCAFFÈ ( (average water content (average water content Minerals (as oxide ash) 8%–12%) 0%–5%) JUNE 2002 COPYRIGHT 2002 SCIENTIFIC AMERICAN, INC. OTHER COFFEE-BREWING TECHNIQUES

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 desired strength. Then press the wire-mesh filter/plunger slowly through

machine emulsifies a small amount of the 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 A broadcast version of this article the grounds create a fine effervescence, oily flavor/fragrance carriers mean that the will air May 28 which is derived from gases (especially great taste and aroma of a good espresso on National carbon dioxide) passing through tiny can be savored for as long as 20 minutes Geographic Today, pores in the cell walls. Some very fine after it has been drunk. Luckily, the a program on the National Geographic grounds can also find their way into the drinker need not know anything about 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 what is called the tiger-skin look. MORE TO EXPLORE The final result is a polyphasic col- Coffee, Vols. 1–6. R. J. Clarke and R. Macrae. Elsevier Applied Science, 1985. loidal system, in which water molecules 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. drink high body, high viscosity and low International Coffee Organization: www.ico.org surface tension. Espresso thus visibly coats International Scientific Association of Coffee: www.asic-cafe.org our tongues and continues to release the Coffee industry–supplied information on coffee, caffeine and health: www.coffeescience.org

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