Tuesday, October 29, 2019

Fermentation of cocoa beans

The beans embedded in mucilaginous pulp are removed from the fruit pods and subjected to microbial fermentation as the first stage in the preparation of chocolate.

Cocoa bean fermentation is still a spontaneous curing process to facilitate drying of nongerminating cocoa beans by pulp removal as well as to stimulate colour and flavour development of fermented dry cocoa beans. The fermentation of cocoa relies on a complex succession of bacteria and filamentous fungi, all of which can have an impact on cocoa flavor.

During cocoa bean fermentation, the role of micro-organisms is limited to removal ofthe pulp that surrounds the fresh beans and the production of indispensable metabolites. The former includes pectin depolymerisation by yeasts. The latter encompasses anaerobic yeast fermentation of sugars to ethanol, microaerophilic fermentation of sugars and citric acid to lactic acid, acetic acid and mannitol bylactic acid bacteria (LAB), and aerobic exothermicbioconversion of ethanol into acetic acid by acetic acidbacteria (AAB). These microbial activities result in the death of the bean due to penetration of mainly ethanol and acetic acid through the husk into the cotyledons.

These biochemical changes inside the beans contribute to the reduction of bitterness and astringency and the development of flavor precursors.

Cocoa flavour precursors are developed during fermentation and drying of cocoa beans. Polyphenols and alkaloids contribute to astringency and bitterness of cocoa and chocolate.

Cocoa beans are mainly fermented in heaps enveloped in plantain leaves or in wooden trays. Yeasts dominate at the beginning, and up to 24 h of fermentation.

Their most important roles are to break down the citric acid in the pulp, which leads to an increase in pH; to produce ethanol and organic acids, which kill the bean cotyledons to produce volatile organic compounds that contribute to precursors of chocolate flavor; and to secrete pectinases, which reduce the viscosity of the pulp and allow aeration of the pulp mass.

Fermentation has several purposes:
*it facilitates removal of the viscous pulp around the beans and their subsequent drying;
*it contributes to colour and flavour development of the nongerminating cocoa beans, as it avoids embryonic growth and activates hydrolytic bean enzymes, enabling the expression of the flavour potential of the cocoa beans genetically and enzymatically
*it reduces bitterness and astringency, in particular by exchange of compounds through diffusion between the cocoa bean cotyledons and the environment.
Fermentation of cocoa beans
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