Double fermentation, sometimes called double washed, involves putting coffee through two distinct fermentation cycles before drying. The cherries are depulped, fermented in water to break down mucilage, washed clean, and then fermented a second time — often under different conditions (temperature, duration, or water chemistry) than the first round.
Why ferment twice?
The second fermentation round serves several purposes:
- Deepens flavor development — additional enzymatic and microbial activity creates more complex precursors
- Refines acidity — the second soak can round out harsh acids while preserving brightness
- Improves consistency — gives producers another control point to dial in the desired profile
Some producers vary the conditions between rounds — for example, a warm first fermentation followed by a cold second soak, or an aerobic first phase followed by an anaerobic second.
What to expect in the cup
- Intensified sweetness — more developed than single-fermentation washed lots
- Complex, layered acidity — citric and malic acids in harmony
- Clean but rich — washed-style clarity with added depth
- Floral and stone fruit — often more expressive than standard washed
Where it’s common
Kenya is the most famous practitioner of double fermentation, where the “Kenya double wash” has long been the standard at top washing stations. The technique is also used by quality-focused producers in Rwanda, Burundi, Colombia, and Ethiopia.