Traditional washed processing ferments for 12 to 72 hours. Extended fermentation runs far longer — 48 hours to a week or more — usually with temperature and pH monitored throughout.
What it does
Longer fermentation produces more of the compounds microbes create, and shifts the profile towards intense fruit, wine and sometimes spirit-like notes.
At its best it produces genuinely remarkable and distinctive cups.
The risk
The line between intense and spoiled is narrow. Over-fermented coffee tastes sour, boozy and vinegary — not complex, just wrong.
Because the process is long, an error compounds. A tank that runs a few degrees warm for a day produces a different coffee from the one intended, and there is no way back.
What separates good from bad
Measurement. Producers running extended fermentation successfully monitor temperature, pH and sometimes Brix continuously, and stop on data rather than on a schedule.
That equipment and expertise is why these lots cost what they do.
The debate
The same one as anaerobic and co-fermentation: does the process reveal the coffee or replace it? Extended fermentation sits in the middle — it uses only what is on the fruit, and it can dominate the origin completely.
Brewing it
Filter, very light roast, clean brewer.