Temperature profiles during the fermentation of Cacao 'Nacional' to understand chocolate quality

Abstract

The quality of chocolate is affected by a multitude of factors including cacao cultivar, maturity, fermentation management, drying, roasting, grinding, conching and, the addition of ingredients. In the sequence of unit operations, perhaps the most complex is fermentation because it is affected by the variability of microbial populations, the variability in the amount of mucilage, and the variability in the concentration of fermentable sugars. Several fermentation studies have been published but very few detail the progress of the fermentation in multiple points in a 1-m3 fermentation box. Both yeast and bacterial fermentations of cacao produce heat. Therefore, we monitored temperature profiles as indirect indicators of microbial activity. Measurement of fermentation temperature at the centre of fermentation boxes and only five other locations in a box have been previously reported. In this research study, we continuously monitored temperature profiles in 27 locations in a symmetric cubic matrix in a 1-m3 box. Temperature right before the removal from one box to the next varied by 10-13 °C for a single batch and up to 16 °C for six batches. The maximal reported temperature was 54 °C. Highest temperatures occurred in the highest layer and lowest temperatures in the lowest layer. However, there was not a clear symmetry in the temperature profiles of the corners in each layer, suggesting non-uniform microbial growth or non-uniform heat losses. Alternation of top and bottom layers when changing from one box to the next reduced the heat non-uniformities. Cut tests at each stage of fermentation indicated the progress of the fermentation is very variable among batches and within a batch. Finally, analysis of headspace volatiles confirms the very large variability of fermentation conditions within and among batches.