Sensory and Physicochemical Characteristics of Two Common Roast Defects in Robusta Coffee

Abstract

Roasting is an important coffee processing step to generate coffee aroma and flavor. Because roasting is time-temperature dependent, the variation of time and temperature applied may influence the structural properties, visual appearance, and chemistry of coffee. Improper roasting creates roast defects that reduce coffee quality and acceptance. Despite this importance, studies on coffee roast defects, particularly in Robusta coffee is limited. This study aims to characterize two common roast defects, i.e., underdeveloped and overdeveloped, compared with medium roast in Robusta coffee. Sensory evaluation by trained panelists and physicochemical evaluation reveal that the two common roast defect in Robusta coffee can be distinguished clearly through differences in sensory (aroma defect) characteristics as well as physicochemical properties. The overdeveloped roast defect produced darker coffee with the highest pH and total dissolve solids (TDS), and can be characterized by pyridine, furan, phenol and pyrrole derivatives. The carbony and ashy notes of the overdeveloped coffee were potentially contributed by phenol and polyphenol derivatives. In contrast to the overdeveloped coffee, the underdeveloped coffee is markedly characterized by higher concentration of aliphatic acids and higher concentration of pyrazines that contributes to raw nut-like notes. The combination of time and temperature during roasting influences the breakdown of chemical compounds through complex mechanisms involving proteins, carbohydrates and polyphenols degradation. Thus, roasting process variations that determine coffee cup quality and in turn drive consumer acceptance should be controlled.