ACIDS IN COFFEE
Green coffee contains many different types of acids, some of which are pleasant to taste and some that are not. Of particular importance to the roaster are the chlorogenic acids (CGAs). One of the key goals of roasting is to try to react these unpleasant acids away without creating negative flavours, or driving off the desirable aromatic components of coffee. Some other acids are stable throughout the roasting process, such as quince acid, which can add a pleasing, clean fresh to coffee.
AROMATIC COMPOUNDS IN COFFEE
Most of the aromatics in a good cup of coffee are created during roasting through one of three groups of processes:
Strecker Degradation - chemical reaction involving amino acids
These are all brought about by the heat during roasting and can result in the creation of over eight hundred different volatile aromatic compounds that flavour the cup of coffee. Although more aromatic compounds have been recorded in coffee than in wine, an individual coffee will only have a selection of these different volatiles. That said, the smell of freshly roasted coffee is so complex that all attempts to manufacture a realistic, synthetic version of this smell have failed.