Reading Smoke Signals: the Roaster's Art

In the world of specialty coffee, the person who transforms green beans into roasted beans has a huge impact on the eventual brew. The smoky aromas and bittersweet flavors that make coffee so alluring don't emerge until beans are roasted.

To paraphrase Timothy Castle, author of The Perfect Cup (Addison Wesley, 1991), roasting is the art of knowing what to conceal and what to reveal. A skilled roaster can highlight the best characteristics in a batch of beans. Working with the same beans, two roasters can produce remarkably dissimilar results. And the outcomes may be equally good, just stylistically different. Like a chef, an expert roaster applies both art and science to the job.

With modern roasting equipment, the roaster can control the temperature and air velocity in the roasting chamber, a rotating drum that keeps the beans constantly moving. The trick is in knowing how long to roast and how hot. Coffee from under-roasted beans has a pasty or bread-like flavor, says coffee expert Kenneth Davids. Over-roasted beans produce coffee that can taste thin, burned or baked. No thanks.

As beans heat up in the roaster, their internal moisture turns to steam and eventually escapes with a sound known as the "first pop." As the roasting continues, the sugar in the bean starts to caramelize, the beans darken, and the aromatic oils begin to volatilize. The so-called "second pop" occurs as these oils expand and rise to the surface. At that point, beans enter what Davids calls "the bittersweet realm of the darker roasts." If the roasting continues beyond the second pop, the beans will steadily lose aroma, acidity and regional character.

Some roasters rely almost entirely on the numbers, with target times and temperatures in mind; others rely more on their senses and alter the roast according to what they are seeing, hearing and smelling rather than what they are measuring. Some skilled roasters say they can judge progress just from the aroma of the smoke, but it's the combination of smell, sound and the appearance of the bean that tell a roaster when the job is done.

Although many consumers believe that dark roasts are superior, that isn't necessarily so. Many connoisseurs prefer a medium roast because it doesn't obscure the signature of the beans' birthplace. It's entirely a matter of taste. Try beans roasted to varying degrees to see where your palate lies.

Light roasts are used mostly for supermarket canned coffee. Light-roasted beans retain moisture so they are heavier and thus more profitable. Medium roast, sometimes known as "full city roast," applies to beans taken just to the point before they become oily. Viennese roast is a dark roast, French and Italian roasts even darker, with espresso roast the darkest of all.

Note that dark roasts don't necessarily produce stronger coffee, as some people think. The proportion of beans to water, not the roast, determines how intense a brew will be.

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