Carbonic Maceration

Carbonic maceration was adapted from the Beaujolais winemaking tradition, where whole grape bunches are fermented in a CO2-rich environment. Coffee producers in Colombia and Costa Rica began experimenting with the technique in the 2010s, drawing directly from winemaking science. The method was popularized by innovative producers like Diego Bermudez of Finca Granja La Esperanza in Colombia, and by Costa Rican farms experimenting with anaerobic techniques. Carbonic maceration coffees gained international fame when they began winning World Barista Championship and World Brewers Cup events, commanding premium prices and generating excitement in the specialty coffee community.

Carbonic maceration involves placing whole, intact coffee cherries in a sealed container and flushing it with carbon dioxide to create an anaerobic, CO2-rich environment. Inside the intact cherries, intracellular fermentation begins. Enzymes within the fruit cells break down sugars in the absence of oxygen, producing ethanol, organic acids, and aromatic esters. Unlike traditional fermentation where microorganisms act on the exterior of the cherry, carbonic maceration triggers an enzymatic breakdown from within the fruit itself. The CO2 environment suppresses the growth of spoilage organisms while allowing the desirable intracellular fermentation to proceed. The result is a unique chemical profile with higher concentrations of fruity esters, floral aromatics, and winey compounds than any other processing method.

1. Selective Harvesting: Only perfectly ripe cherries are hand-picked. Uniform ripeness is critical because the fermentation depends on intact, healthy fruit. 2. Sorting and Flotation: Cherries are sorted by density in water tanks. Floaters (less dense, lower quality) are removed. Only sinkers proceed. 3. Container Loading: Intact whole cherries are loaded into stainless steel or food-grade plastic tanks. The cherries are NOT depulped, which distinguishes carbonic maceration from other anaerobic methods. 4. CO2 Flushing: The tank is sealed and flushed with carbon dioxide gas, displacing oxygen. A one-way valve allows CO2 to escape as fermentation produces more gas, but prevents oxygen from entering. 5. Fermentation: The cherries ferment in the CO2-rich environment for 24 to 200+ hours. Temperature is monitored and may be controlled. The intracellular enzymatic fermentation produces ethanol, acids, and aromatic compounds. 6. Monitoring: pH, temperature, and time are monitored. The tank may be opened periodically for sampling. Target pH drop is to approximately 3.5 to 4.0. 7. Removal: After the desired fermentation time, cherries are removed from the tank. 8. Processing: The fermented cherries are then processed using a secondary method, typically washed, honey, or natural. The carbonic maceration stage is the primary flavor driver, but the secondary processing still affects the final cup. 9. Drying: Coffee is dried on raised beds or in mechanical dryers to 10 to 12% moisture. 10. Resting and Hulling: Coffee rests in parchment for 30 to 60 days, then is hulled and sorted for export.

Carbonic maceration is defined by its unique fermentation. Whole, intact cherries are placed in a CO2-rich, oxygen-free environment. Inside each cherry, intracellular enzymes (not external microorganisms) break down sugars, producing ethanol, lactic acid, acetic acid, and aromatic esters. The CO2 environment suppresses spoilage organisms while allowing the enzymatic fermentation to proceed. Fermentation time ranges from 24 to 200+ hours, with longer times producing more intense flavors. The pH drops from approximately 5.5 to 3.5 to 4.0. Temperature control (18 to 25 degrees Celsius) is important for consistent results. The specific flavor compounds produced depend on time, temperature, cherry ripeness, and the coffee variety.

After carbonic maceration fermentation, the coffee is dried using the producer's preferred secondary method. Most commonly, the fermented cherries are depulped and washed, then dried on raised beds for 10 to 20 days to 10 to 12% moisture. Some producers use natural (dry) or honey processing as the secondary method. The drying stage must be carefully managed, as the fermented coffee can be more delicate. Mechanical drying at controlled temperatures may be used in humid conditions. Target moisture is 10 to 12%.

Carbonic maceration coffees should be stored in breathable bags during the parchment stage, then in GrainPro or hermetic bags for green coffee. The intense, delicate flavors developed during carbonic maceration may fade with aging, so these coffees are best consumed within 6 to 12 months of harvest. Store at 15 to 25 degrees Celsius with 50 to 60% relative humidity.

• •Produces intensely fruity, complex, and winey flavor profiles unlike any traditional method
• •High control over fermentation through CO2 environment, time, and temperature
• •Creates distinctive, competition-winning coffees that command premium prices
• •Suppresses spoilage organisms through the CO2-rich anaerobic environment
• •Allows producers to differentiate their product in a competitive market
• •Can enhance specific desirable flavor notes like tropical fruit, berry, and floral

• •Requires specialized, expensive equipment (sealed tanks, CO2 systems, monitoring tools)
• •High risk of over-fermentation if not monitored carefully
• •Inconsistent results, especially without temperature control
• •Can produce polarizing, overly fermented flavors that mask terroir
• •High labor and skill requirements for monitoring and quality control
• •Higher production cost translates to higher consumer prices
• •Requires perfectly ripe cherries, demanding careful selective harvesting

Carbonic maceration produces some of the most distinctive flavor profiles in coffee. Common descriptors include: intense tropical fruit (mango, pineapple, passion fruit), berry and stone fruit, winey and alcoholic notes, floral and perfumed aromatics, candy-like sweetness, and a heavy, syrupy body. Acidity is often perceived as fermented or winey rather than citric. The flavors can be so intense that they completely mask the coffee's inherent terroir, which is controversial in specialty coffee. Well-executed carbonic maceration produces complex, balanced intensity; poorly executed versions taste over-fermented, solvent-like, or rotten.

• •Over-fermentation from extended maceration, producing rotten or solvent-like flavors
• •Inconsistent fermentation causing batch-to-batch variation
• •Loss of terroir, where the coffee's inherent character is masked by processing flavors
• •Contamination from unwanted microorganisms if the seal is compromised
• •pH dropping too low, causing excessive, unpleasant acidity
• •Oxygen entering the tank if the seal fails, causing aerobic spoilage

Carbonic maceration uses moderate water for secondary processing and flotation. The CO2 used is typically food-grade and produced industrially. The sealed tanks reduce environmental exposure. Fermentation byproducts (CO2, organic acids) are released or contained. The main environmental consideration is the energy required for CO2 production and potential temperature control equipment. Overall impact is similar to other processing methods, with the primary difference being equipment investment.

• •Temperature-controlled fermentation tanks for precise management
• •Combination with yeast inoculation for consistent, repeatable flavor profiles
• •Multi-stage carbonic maceration with different conditions at each stage
• •Use of specific yeast strains (Saccharomyces cerevisiae, Torulaspora delbrueckii) alongside CO2
• •Blending carbonic maceration lots with traditionally processed coffees for balance
• •Short-duration carbonic maceration (24 to 48 hours) for more subtle flavor modulation

• •Chapter 2: Processing Methods
• •Chapter 5: Extraction Science

• •Specialty Coffee Association
• •Coffee Science Foundation
• •Diego Bermudez / Finca Granja La Esperanza
• •World Coffee Research