The Development of Coffee Flavor

The hotter the bean is roasted, the darker it gets, and its color is a good indicator of flavor balance. In the early stages of roasting, sugars are broken down into various acids (formic, acetic, lactic), which together with their own organic acids (citric, malic) give light-brown beans a pronounced tartness. As roasting proceeds, both the acids and astringent phenolic materials (chlorogenic acid) are destroyed, so acidity and astringency decline. However, bitterness increases because some of the browning-reaction products are bitter. And as the bean’s color becomes darker than medium brown, the distinctive aromas characteristic of prized beans become overwhelmed by more generic roasted flavors—or, conversely, the flavor deficiencies of second-rate beans become less obvious. Finally, as acids and tannins and soluble carbohydrates decline with dark roasting, so does the brew’s fullness of body: there’s less there to stimulate our tongue. Medium roasts give the fullest body.