Evolution of coffee aroma characteristics during roasting

The purpose of this study was to correlate the global aroma of ground coffee (Columbia) with the relative composition of its odorous components at various roast levels, ranging from green to over-roasted coffee. Roast levels were chosen to produce distinct aromas (roasting at constant temperature, from 1 to 9 minutes). The aroma of the various coffees was characterised by sensory profiling using the "Champ des Odeurs" approach. Volatile compounds were recovered by steam vacuum distillation, followed by solvent extraction and concentration. The odour representativeness of the extracts was checked by sensory similitude tests. Odorous compounds were characterised by GC-O (CHARM technique) and identified and quantified by mass spectrometry. A good agreement between the assessors was found for describing the odour of various ground coffees. Out of the 26 descriptors, 16 were characterised as relevant to differentiate the coffee samples. Fatty, green, lactone and terpenic notes were representative of the green coffee. During roasting, sweet notes, pyrogenic sulphurous and finally amino odours were developed. The evolution of the sensory intensities was compared to the generation of volatile compounds presenting similar odorous characteristics. Green and earthy notes in the overall aroma of roasted coffees were equal or lower in intensity as compared to their level in green coffee while the concentration of associated volatile compounds remained unchanged or increased during roasting. Most of the sweet notes presented a maximum of intensity for both the sensory assessment and concentrations of associated compounds. However the concentration maximum occurred at higher roast levels (4-6 minutes for concentration maximum, 1-2 minutes for sensory maximum). The evolution of roasty notes was found to be partly correlated with that of roasty-smelling compounds. Sulphurous and smoky notes were better correlated with associated compounds, and are certainly at least partially responsible for the masking effect in the perception of sweet, green and earthy notes of roasted samples.