3. Post-harvest

a.) Fermentation

Fermentation is normally carried out in heaps or boxes and is a crucial stage in the development of the cocoa flavour precursors. Moreover, fermentation is recommended to avoid ochratoxigenic fungal growth and OTA production because acetic, lactic and citric acid produced by bacteria during fermentation can inhibit these undesirable fungal species. Research has shown that OTA production can increase if wet beans, or partially depulped beans, are allowed to ferment during drying on a drying mat.

The fermentation process can be influenced by factors such as the variety of cocoa, addition of starter cultures of micro-organisms, altering the pulp:bean ratio, aeration and frequency of turning though in most cases good quality beans can be obtained by simply allowing the fermentation to proceed for between three to five days with a single turn after 24 and 36 hours to ensure uniformity. Lack of fermentation or under-fermentation will give rise to slaty and purple beans with consequent increases in bitterness and astringency. Although fermentation over 5 to 6 days is quite common in West Africa, extending fermentation beyond 120 hours in some situations brings a danger of over-fermentation with loss of cocoa flavour and development of off- flavours from putrefaction. 

Traditionally, some “fine flavour” cocoas require shorter periods of fermentation. Although modern cocoa estates may carefully control the fermentation conditions, in smallholder production systems it is more of an art than a science. Farmers often assess the progress of fermentation by cutting a few beans at intervals to observe the colour changes and judge the end-point on the smell and the external appearance of the beans, together with well-defined internal ridging on cut beans, which through experience will indicate that they are ready to be dried.

Fermentation heaps or boxes should include wet beans from sound pods that are sufficiently ripe to allow the individual beans to be separated easily by hand from the placenta and husk. Damaged and diseased beans, pieces of husk and placenta should be separated and discarded.

Any baskets, trays or platforms used for the fermentation, and any tools such as paddles and shovels, should be maintained reasonably clean and dry between fermentations. Care should be taken to prevent cocoa beans from coming into contact with water during fermentation. A covered and/or sheltered space should be chosen to provide adequate protection against rain, wind and direct sunlight.

The fermentation process generates a considerable heat and temperatures close to 50°C can be reached within the mass of beans during fermentation. The fermentation of very small quantities of beans will allow the heat to dissipate and the fermentation will be unsatisfactory. The minimum quantity of wet beans for a normal fermentation is considered to be about 100kg, although, as described in Appendix B, there are methods for fermenting smaller quantities of cocoa which are suitable for experimental purposes. 

Heaps of between 250 and 500kg are typical in West Africa, while in Southeast Asia and Brazil where box fermentation is practised, bed depths of between 40 and 100cm are normal with quantities being between 500 and 2,000kg of wet beans.

Ferments very much larger than 2,000kg are difficult to manage in order to achieve uniform and effective fermentation. For practical reasons, therefore, about 2,000kg wet beans is considered to be the upper limit for a single fermentation.