What is co-fermentation in coffee processing?

Co-fermentation is a processing method where natural ingredients - fruit, spices, botanicals, herbs - are added directly into the fermentation vessel alongside the coffee. The aim is for those additions to influence the microbial environment and interact with the bean, imparting additional flavour compounds during fermentation.

Common additions include cinnamon, passionfruit, citrus peel, and banana. The added ingredients contribute sugars, acids, and aromatics that fermenting microorganisms incorporate into their metabolic activity, which the bean then absorbs.

The results can be striking - sometimes explicitly reflecting the added ingredient. Co-fermented coffees divide opinion: proponents see them as an extension of fermentation craft; critics question whether the result is genuine coffee character or something imposed from outside. Done well, the added element enhances without dominating. Done poorly, it produces clashing or artificial flavours that overwhelm the underlying coffee.