Postharvest Treatment of Cocoa Changes Aroma of Dark Chocolate

After cocoa beans are harvested, they are traditionally covered in banana leaves and left for a few days to ferment. During this time, microbes degrade the pulp surrounding the beans, raising the temperature and acidifying the beans. This causes changes in the beans that help to develop the pleasing flavors and aromas associated with chocolate.

In an alternative, non-microbial treatment approach called moist incubation, dried unfermented cocoa nibs are rehydrated in an acidic solution, heated for 72 hours, and then re-dried. This method is faster and more easily controlled than fermentation. It produces aromas in beans that are similar to those achieved via fermentation, with some differences.

Irene Chetschik, Zurich University of Applied Sciences, Wädenswil, Switzerland, and colleagues have investigated how the taste and aroma of chocolate compare when using either moist incubation or traditional fermentation. The researchers made dark chocolate bars using either moist-incubated or fermented dried cocoa beans, as well as unfermented beans as a control. Sensory panelists found that the moist-incubated samples had higher intensities of fruity, flowery, malty, and caramel-like aromas. The fermented samples had higher scores for “roasty” aroma notes. The bar made from unfermented beans had a primarily “green” aroma. The panelists rated the moist-incubated sample as the sweetest-tasting, while the unfermented chocolate was the most bitter and astringent.

Identification of aroma compounds by gas chromatography (GC)-olfactometry and their subsequent quantitation by GC-mass spectrometry showed higher levels of malty compounds called Strecker aldehydes and lower amounts of “roasty” pyrazines in the moist-incubated chocolate compared with the fermented one. The researchers concluded that the moist incubation process creates chocolate with a pleasant aroma and taste and could, therefore, serve as an alternative postharvest treatment.