Carbonic Maceration
Sources: Tim Wendelboe (website)
Carbonic maceration (CM) is a coffee processing technique adapted from winemaking in which whole, intact coffee cherries are placed in sealed, pressurised vessels filled with carbon dioxide (CO₂). The anaerobic, CO₂-rich environment drives intracellular fermentation — fermentation that occurs inside the cherry cell walls rather than by microbial action on the surface — producing a distinctive and typically intense flavour profile.
Process
- Harvest: Ripe cherries selectively picked and sorted; unripe and damaged cherries removed.
- Loading: Whole cherries (not depulped) loaded into sealed tanks.
- CO₂ purge: Tanks are sealed and flushed with CO₂ to eliminate oxygen, creating an anaerobic environment.
- Fermentation: Intracellular fermentation proceeds inside the intact cherries for a defined period (hours to days depending on target flavour profile and temperature).
- Drying: After CM fermentation, cherries are removed and dried — typically on raised beds.
Variations include semi-carbonic maceration (partial CO₂ environment) and combining CM with honey or natural drying stages.
Cup Profile
Carbonic maceration produces coffees with:
- Intense, often wine-like or spirit-like fruit character
- High aromatic complexity
- Unusual fermentation-derived compounds (esters, alcohols)
- Distinctive acidity profile — often bright but with more complexity than standard washed coffees
- Polarising for tasters who prefer clean, “true to cultivar” profiles
The CM method sits at the experimental end of processing — producing coffees that are immediately identifiable and market-differentiating, but require careful execution to avoid off-flavours.
At Finca Los Pirineos
Finca Los Pirineos (Diego Baraona, Usulután, El Salvador) offers carbonic macerated coffees among its processing options. However, Tim Wendelboe — the farm’s primary long-term buyer — does not purchase CM lots, preferring semi-washed and honey processed coffees for cleaner, “true to cultivar” flavour. (source: Tim Wendelboe (website))
This illustrates that CM production is market-dependent: the technique attracts certain buyer segments (those seeking experimental or differentiated cups) while remaining unappealing to buyers who prioritise varietal purity and terroir expression.
Relation to Other Fermentation Methods
See Coffee Processing for the full processing method taxonomy, including:
- Natural (dry process)
- Washed (wet process)
- Honey / Pulped natural
- Anaerobic fermentation — similar oxygen-exclusion principle, but without CO₂ pressurisation and usually applied to depulped beans
- Lactic fermentation — inoculated with specific bacterial strains
Carbonic maceration and anaerobic fermentation are sometimes conflated; the key distinction is that CM uses whole cherries and CO₂ pressurisation, while standard anaerobic fermentation typically uses depulped beans in sealed tanks without active CO₂ injection.