The pulp-coated seeds are placed into a fermentation box, traditionally lined with banana leaves. They’re left to ferment for 3-7 days depending on cacao type. The seeds are often called cacao beans at this stage, and some farmers sort cacao beans by size or pod color before fermenting. During fermentation, the sugars in the pulp surrounding the seeds are consumed by local yeast and bacteria, changing the composition of the beans.
Temperatures inside fermentation boxes can reach 50 degrees Celsius; any higher and it can damage the beans, but any lower and fermentation won’t complete. Fermentation is crucial to chocolate making, as it’s the point at which beans develop the flavor precursors typically associated with cocoa. These flavors are enhanced during roasting, but fermentation lays the foundation. Beans are usually turned multiple times during fermentation, to ensure that all cacao is equally fermented, and the temperature doesn’t rise too high too quickly.
On the other hand, some farmers don’t ferment their beans at all, choosing to immediately dry them in the sun. This is a problem because of fermentation’s crucial role in flavor development. Those unfermented beans will lack a complex and chocolatey flavor at later steps of chocolate making, as well as often being overly bitter and astringent.