A Cupful Of Coffee Science – Part One

From a chemical point of view, espresso is a solution, an emulsion, a colloidal suspension and an effervescence, all at the same time. Basically, it is a small miracle of chemistry and physics.

Wellcome Images/Annie Cavanagh – www.wellcomeimages.org

Let’s have a cupful of coffee science.

For sheer sensory enjoyment, few everyday experiences can compete with a good cup of coffee. The alluring aroma – further enhanced through preservation in illy’s pressurized cans – of steaming hot coffee just brewed from freshly roasted beans can drag sleepers from bed and pedestrians into cafés. And many millions worldwide would find getting through the day difficult without the jolt of mental clarity imparted by the caffeine in coffee.

Connoisseurs agree that the quintessential expression of coffee is espresso: that diminutive, heavy china cup half-filled with a dark, opaque brew topped by a velvety thick, reddish-brown froth called crema. Espresso—the word refers to a serving made on request expressly for the occasion—is brewed by rapidly percolating a small quantity of pressurized, heated water through a compressed cake of finely-ground roasted coffee. The resulting concentrated liquor contains not only soluble solids but also an array of aromatic substances in a dispersed emulsion of tiny oil droplets, which together give espresso its uniquely rich taste, smell and “mouthfeel.”

Coffee cultivation entails myriad variables that must be monitored and regulated. For a single portion of espresso, 50-55 roasted coffee beans are required. A single imperfect bean will noticeably taint the whole. Only through modern technology can 50 nearly perfect beans be economically and consistently identified. At illycaffè beans are checked one by one through an electronic selection system that can process hundreds of beans per second to avoid that even one bean could alter the taste of the blend.

Of the over 100 coffee species of the genus Coffea that exist, two species are commercially exploited: Coffea arabica, which accounts for two thirds of world production; and Coffea canephora, often called robusta coffee, with one third of global output .

Coffee Cup With Beans

Arabica is a medium- to low-yielding, rather delicate tree standing 5 to 6 meters tall that requires a temperate climate and considerable growing care. Coffee made from arabica beans has an intense, intricate aroma that can be reminiscent of flowers, fruit, honey, chocolate, caramel or toasted bread. Its caffeine content never exceeds 1.5 percent by weight. Because of its superior quality and taste, arabica sells for a higher price than its hardy, rougher cousin.

The ultimate quality of the coffee beans depends on the genetics of the plant, the soil in which it grows, and the microclimate. Along with the roasting processes which are applied (and which I will address in my next blog), these agronomical and geographical considerations are responsible for the taste differences among the many coffee beans that roaster combine to produce the various distinctive blends.

 

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