Résumé
The purpose of our work was to examine the impact of four wet processing methods on the quality of roasted coffee, with three degrees of roasting. The volatile fraction of the coffees was analysed by combining Headspace-SPME (HS-SPME), GC-olfactometry (GC-O) and mass spectrometry (GC-MS). Post-harvest processing has a major impact on the aroma quality of the roasted coffees produced by those processes. This was more or less acknowledged for differentiating between the dry and wet methods. Our work has shown that modifications to the wet method also lead to aromatic differences in roasted coffees. Coffee produced by the traditional wet method was of better aromatic quality than coffee produced by the mechanical method recently introduced because it uses less water and is more ecological. Indeed, this last aspect resulted in coffees with more aroma defects. The fact of carrying out microbial mucilage removal in water or under dry conditions also led to differences between the coffees. Mucilage removal in water gave coffees with more particular fruity, floral and caramel attributes, whereas dry mucilage removal gave more neutral coffees. When the latter process was also combined with dry pulping, sourness defects occurred with light roasting and those coffees developed bitterness and harshness with darker roasting. Light roasting made it possible to more effectively distinguish between treatments based on aroma criteria associated with the volatile compounds produced during post-harvest processing. Dark roasting also enabled a distinction to be made, but based on aromatic criteria linked to the thermal reactions of roasting. Medium roasting enabled the least distinction to be made between treatments, undoubtedly because a higher degree of roasting cancelled out the olfactory differences detected with light roasting, which were associated with highly volatile compounds, such as esters, and because that degree of roasting was not yet high enough to give aroma and sensory differences associated with roasting. The next stage in this work will be to analyse volatile compounds of green coffee produced during post-harvest processing, along with chemical compounds that are precursors of the thermal aroma that develops during roasting, and which also play a role in the taste of roasted coffee, in order to gain a clearer understanding of the differences seen in our work on roasted coffee. (Résumé d'auteur)