Fermentation is a confusing coffee term with two main meanings:

1) In the wet method of coffee processing, fermentation is a stage in which the sticky pulp is loosened from the skinned coffee seeds or beans by natural enzymes while the beans rest in tanks. If water is added to the tanks the process is called wet fermentation; if no water is added it is called dry fermentation.

2) In sensory evaluation, or cupping, of coffee, fermentation is an important descriptor for a range of related taste defects set off when the sugars in the coffee fruit begin to ferment (by micro-organisms). Sensations described as fermented can range from sweet, compost-;like, rotten-fruit tastes to mouldy, musty, or medicinal tastes.