Anaerobic Green Coffee Beans

Coffee is sealed in tanks or bags fitted with one-way valves. CO₂ produced by fermentation pushes the oxygen out and escapes, while no air gets back in. Without oxygen, different microbes take over – often lactic acid bacteria and yeasts – and fermentation runs slower and more controllably, so producers can extend it for days. The coffee is then washed or dried directly, depending on the protocol. See anaerobic fermentation in our glossary and our guide to coffee fermentation.

Anaerobic lots carry plenty of fermentation-derived aromatics that are easy to roast away or exaggerate. Most roasters keep them light to medium-light and avoid long development, which can push the fruit into boozy, vinegary or ashy territory. Anaerobic naturals often colour quickly, so go gentler early on. Cup at two roast levels before committing – the gap between vibrant and overdone can be small.

In an anaerobic natural the whole cherry ferments in the tank and is then dried, so the bean takes on more from the fruit – expect jammy, tropical, sometimes heady cups. In anaerobic washed lots the cherry is depulped first, giving cleaner, more structured cups with fermented fruit layered on top. Carbonic maceration is a specific anaerobic method using a CO₂-filled tank, and many lots here also appear under extended fermentation.

Most of our anaerobic lots come from Colombia, Peru, Mexico and Ecuador, where producers have invested in tanks and protocols, plus anoxic naturals from Mexico and South Sudan. See our wider fermented and experimental ranges for yeast-inoculated, co-fermented and thermal shock lots.