Influence of drying on cocoa aroma development

A general cocoa aroma development diagram was presented at ChocoTecnic'98. The diagram enabled characterization of the relative sizes of the volatile fractions of thermal or non-thermal origin. However, it was based on dried cocoas and could therefore not be used to distinguish between the respective roles played by fermentation and drying. To that end, a set of experiments was conducted under a cooperative project with Venezuela on Criollo cocoa aroma quality. As these are very recent results, we shall present them without going into reaction mechanism aspects. Cocoas were fermented in cubic (60 cm) wooden boxes for 4 days. The following fermentation conditions were studied. - 2 pod opening delays: 0 days and 5 days, - 3 turning rates: every 24 h, after 48 h, and after 24 and 72 h, - 3 harvest dates per pod opening delay. A sample was taken each day and divided into 2 parts; one was frozen at -80°C, the other was sun-dried. Volatile compounds were extracted by steam distillation and analysed by GC-MS (DB Wax column, 60 m x 0.32 mm). The fermentation time and harvest date were the only two factors that caused any significant differences in volatile compound contents between the experiments, the former being by far the more important. Fresh Criollo cocoa beans contained a qualitatively very large volatile fraction: 94 compounds were characterized. During cocoa drying, 26 new compounds appeared. This volatile fraction was much more developed than that of Forastero cocoas. During fermentation, it was primarily the alcohol and acid fractions that developed. The overall aldehyde, pyrazine, furan and phenol contents were in much smaller quantities and increased steadily during this operation. When compounds were considered individually, their contents evolved in several ways: 56 remained constant, 7 decreased, 19 increased and 10 followed a bell curve. The effect of drying was measured by the variation in volatile compound contents before and after drying. For instance, during this operation, overall alcohol contents (particularly ethanol) and acid contents (mainly acetic) decreased substantially. The aldehyde, ketone, pyrazine and pyrrole contents increased after one day's fermentation, whereas the phenol content and, to a lesser degree, the ester content decreased. Taken individually, the compound contents evolved in different ways: 43 appeared, 32 remained constant, 2 decreased, 73 increased and 11 followed a bell curve. The initial results of an analysis of the volatile fractions of cocoa sampled daily during 8 days of drying indicated that changes during drying were complex. (Résumé d'auteur)