Bacterial boost for Canephora fermentation
How lactic acid bacteria change quality
Less caffeine, more antioxidants, clearer content. A new study shows how targeted fermentation can improve Robusta.
Canephora is our passion. We work to improve how Canephora is perceived. Precision fermentation is a key lever. A recent study in Biodiversitas shows that adding the lactic acid bacterium Leuconostoc mesenteroides during wet fermentation improves the quality of Robusta coffee beans. The inoculation reduced caffeine and increased antioxidant properties. It did so without affecting flavor.
Contents of the study
Measured
pH, caffeine, total phenolic content, antioxidant activity, baseline parameters, microbiology, and a sensory panel evaluation.
Objective
Assess the impact of a defined starter culture on the chemistry, safety, and sensory quality of Robusta.
Design
Wet fermentation for 6, 12, and 18 hours, each with and without starter. Analyses on samples before and after roasting.
Effects
- Caffeine decreased by about 13 percent on average.
- Total phenolics increased and antioxidant activity rose.
- pH decreased due to organic acid formation.
- Sensory notes included dark chocolate, caramel, and a rounded mouthfeel.
Sweet Spot
Twelve hours of fermentation with starter delivered the strongest chemical and sensory results.
Practical application
Set up micro batches, log pH and temperature, prioritise 12 hours, and share results transparently.
Takeaway
Targeted microbiology can shift how Canephora is perceived. Quality is not an accident.
The fermentation process. Leuconostoc mesenteroides as a driver of quality
Post harvest coffee processing proceeds through either dry or wet fermentation. Wet fermentation immerses the beans in water and can increase antioxidant activity, likely due to spontaneously present lactic acid bacteria.
In this context Leuconostoc mesenteroides was applied as a bacterium with proteolytic activity that plays a key role in caffeine breakdown and in increasing antioxidant activity.
Key roles of L. mesenteroides
- Caffeine degradation: L. mesenteroides shows enzymatic activity that degrades caffeine, that is 1,3,7 trimethylxanthine, through demethylation. The pathway yields compounds such as 3,7 dimethylxanthine, 7 methylxanthine, and xanthine. The bacterium can reduce caffeine by more than 89 percent and produce paraxanthine. Paraxanthine is considered safer than caffeine since it shows no toxicological effects in rats.
- Antioxidant release: The bacterium expresses enzymes such as feruloyl esterase and tannase. Feruloyl esterase can liberate antioxidant compounds like ferulic acid and hydroxycinnamates from cell walls. Tannase also contributes to total phenolic content.
- Acid formation: As a heterofermentative organism L. mesenteroides produces organic acids, including acetic, lactic, citric, and malic acid. This acid production lowers pH in both green and roasted coffee beans.
The chemical balance. Less caffeine, more protection
The results of the study, which examined Robusta coffee from Mount Merapi in Yogyakarta, Indonesia, show significant shifts in chemical composition:
| Quality characteristic | Effect of adding L. mesenteroides | Details |
|---|---|---|
| Caffeine amount | Significant reduction | The caffeine level in coffee beans was reduced by an average of 13.34% through the addition. In espresso made from roasted beans, the level ranged from 2.05 to 3.04%. |
| Antioxidant activity | Significant increase | Activity increased by approximately 1.06%. Traces of L. mesenteroides at 12 hours of fermentation showed the highest antioxidant activity. |
| Total phenolic content (TPC) | Increased | The TPC increased due to the enzyme activity (feruloyl esterase and tannase) of the LAB. In roasted beans, the TPC ranged between 85.37 and 123.87 mg GAE/g. |
| Protein content | Reduced | The proteolytic activity of L. mesenteroides led to a reduction in the protein content of the green beans. |
| pH-level | Sunk | The formation of organic acids by the bacteria led to a more acidic profile. |
| Moisture content | Complies with national standards | The moisture content tended to decrease and ranged between 9.82% and 10.83% for green beans (norm: <12.5%) and between 3.33% and 3.80% for roasted beans (norm: <5%). |
Sensory. Improved flavor
The addition of L. mesenteroides also improved the sensory properties of espresso from roasted beans. Compared with the control group, professional baristas rated flavor, aroma, and mouthfeel higher for the fermented lots.
This effect is linked to the formation of acetic, citric, lactic, malic, and succinic acids during wet fermentation. The treatment intensified the perception of dark chocolate and led to the development of caramel notes, which is attributed to a higher carbohydrate content in the green beans.
Conclusion
In summary, adding L. mesenteroides during wet fermentation of Robusta coffee produced significant shifts in chemical quality. Protein and caffeine decreased, and pH declined. Total phenolic content and antioxidant activity increased.
The strongest gains in bioactive compounds and the best sensory scores were achieved with twelve hours of fermentation with L. mesenteroides.
This approach offers a promising pathway to make Robusta both healthier and more sensorially complex by harnessing lactic acid bacteria. Even very small microbial helpers like L. mesenteroides can have a large impact on the quality of everyday coffee.
Further research
The study suggests that testing additional LAB strains in coffee beans could further unlock these potential health benefits.
Key findings translated into practice
1) Caffeine decreases measurably
- Average reduction of about 13 percent with the starter.
- Example values in roasted samples. Peaks around 2.0 to 2.1 percent caffeine with starter at longer fermentation compared with up to about 3.0 percent without starter.
- Implication: Robusta stays strong yet tastes gentler. Espresso blends gain flexibility in recipe design.
2) Greater antioxidant potential
- Total phenolic content TPC increases significantly, with the strongest gain at twelve hours with starter.
- Antioxidant activity rises slightly. Roasting adds further activity through Maillard reaction products.
- Implication: Potentially more stable and clearer cups and better shelf robustness.
3) Clean and safe
- Post roast microbiological counts are well below common limits. The starter also acts through competitive exclusion.
- Implication: Process safety remains high, even with longer durations.
4) Sound sensory performance
- Six to twelve hours with starter scored best in the panel. Dark chocolate and caramel notes with pleasant viscosity. Color was perceived slightly darker.
- Implication: A profile that fits our Canephorum flavor arc.
Limitations of the study
The findings are based on a specific green coffee matrix and defined laboratory conditions. Results may vary by origin, cultivar, native microbiota, and process setup. Caffeine values reported as percent or mg per mL do not translate directly to a brewed cup. We remain conservative in statements to consumers.
Sources
Rosaliana, F., Swasti, Y. R., & Purwijantiningsih, E. (2025). The quality of robusta coffee (Coffea canephora) with the addition of Leuconostoc mesenteroides during wet fermentation. Biodiversitas, 26(7), 3334–3342. doi: 10.13057/biodiv/d260725.
