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This article is about the study of the diffusion of water and acetic acid in a grain of cocoa in course of drying. The authors present a method of microanalysis which enables the analysis of each little slice of the grain : a precise measurement of each slice is realised in view of the analysis from the centre to the surface of the grain with the aid of a cutting apparatus, designed and realised to this effect. At each instant of the drying process, the profiles of water and acetic acid contents are then determined. A one dimensional diffusion model enables a shell by shell evaluation of the diffusion of water and acid in the cocoa grain. The results obtained show an augmentation of transport coefficients in course of drying. We however observe a decrease of the diffusion coefficient of water to the low moisture content : what makes us think of the appearance of crusting phenomenon.

A study was carried out of the changes in moisture and acetic acid contents during the fermentation and convection drying of cocoa beans. A laboratory drier operating by convection or conduction and a series of three volatile acidity extractors based on the Mothe-Efter method were used. An original cutting system made it possible lo analyse five inner layers of cocoa bean from the centre to the outside edge. Processing of the results enabled the determination of the local and overall changes in the moisture and acetic acid contents and showed the influence of air parameters on drying in thin layers.