At its best, it can also be richly flavored with winy notes, moderate acidity and medium body. Because coffee beans are a complex combination of components, what happens in the roasting process is not entirely understood. Essentially, roasting releases moisture in the beans and brings oils to the surface. As roasting continues, more oil exudes from the beans, which is why dark-roasted beans look as if they've been lubricated with motor oil. Sugars are burned, making darker roasts more caramelized in flavor.
Caffeine is burned up, too.
Most roasting equipment is fairly primitive because the technology of coffee lags far behind that of wine. Dallis Brothers uses a drum roaster, circa 1940, that looks like a miniature steam locomotive. When to take the beans out depends on the style and skill of the roaster. West Coast roasters typically roast darker than those in the East. Peet's, the legendary San Francisco Bay Area roaster and retailer, probably roasts its beans darker than anyone in the country.