Skip to content
PPXLROASTERS
PXL Roasters
  • History
    • Topic XX

    Fermentation

    Between the picked cherry and the green bean, a few hours or a few days go by during which nobody touches anything, and during which everything is decided. Microorganisms eat the sweet flesh that sticks to the bean, give off acids, alcohol and gas, and leave behind a coffee that no longer tastes the same. This plate explains what really happens in the tank, who does it, how we know it is done, what goes wrong, and what science has actually shown. It reads at two depths: the running text uses no trade word without explaining it, and each section opens onto a folded development for those who want the strains, the kinetics and the disagreements.

    A food-grade plastic fermentation jug closed by a lid pierced with a water airlock filled with liquid, a hand holding a price tag in front
    Plastic fermentation jug closed by an airlockKVDP, 2008-07-16, Public domain

    The 10 sections of this plate

    Each section has its own page. The first sentence says what you will find there.

    1. 01What we call fermentingA coffee cherry is a pit surrounded by sugar.
    2. 02What ferments, and what does notThis point is the most important of the plate, and the one most often wrong in what is read.
    3. 03Who does the workNobody puts them there. The microorganisms arrive with the cherry: they are on the skin of the fruit, on the hands, on the tanks, in the water.
    4. 04What happens, hour by hourAn ordinary washed fermentation lasts between twelve and thirty-six hours.
    5. 05Who really detaches the sweet fleshHere is the question everyone answers, and nobody has settled.
    6. 06“Anaerobic,” the most misused word in the tradeAnaerobic means “without air.” When a coffee is sold as anaerobic, one imagines a tank from which the oxygen has been driven out.
    7. 07Knowing when it is doneThis is the real skill of the trade, and it still depends a great deal on the hand.
    8. 08What goes wrongA fermentation does not degrade progressively, it tips over.
    9. 09What fermentation really changes in the cupHere one must be careful, because this is the ground where the most is claimed and the least is measured.
    10. 10What we do not knowAn honest plate ends with its gaps.

    Elsewhere on the site, the passages that deal with the same things as this page. Computed from the text, not picked by hand.

    Process sheetCarbonic macerationBoth mention carbonic, maceration and anaerobic.Process sheetMicro-oxygenationBoth mention maceration, carbonic and fermentation.Process sheetSelected yeastsBoth mention yeasts, inoculation and mucilage.The processesAnaerobic and SIAF: nobody drives out the airBoth mention anaerobic, SIAF and carbonic.Process sheetKoji and fungal fermentationsBoth mention yeasts, inoculation and acid.Process sheetExtended fermentationBoth mention mucilage, acid and fermentations.
    © 2026 Marco De Sousa Rosa · PXL RoastersTexts under CC BY-NC-SA 4.0 · tools: all rights reserved · images: see the provenanceHome · Colophon · Site map