The role of microorganisms in robusta coffee fermentation and its impact on sensory quality

Abstract

Robusta coffee (Coffea canephora) is one of Indonesia’s strategic plantation commodities, contributing significantly to national coffee production. Although highly productive, the sensory quality of Robusta coffee is often considered inferior to Arabica, particularly in terms of aroma, acidity, and complexity of flavor. One effort that can be made to improve the quality of Robusta is through post-harvest fermentation. Fermentation is a biological process involving microorganisms in breaking down the mucilage layer on the beans, while producing metabolites such as organic acids, ethanol, and volatile compounds that greatly affect the flavor and aroma profile of coffee. This study aims to examine the role of microorganisms in Robusta coffee fermentation and their contribution to improving sensory quality. Various studies show that the dominant microbial groups include yeast, lactic acid bacteria (LAB), and acetic acid bacteria (AAB). Yeast produces ethanol and aromatic volatile compounds, LAB produces lactic acid which lowers the pH and adds a fresh taste, while AAB oxidizes ethanol into acetic acid, which affects acidity. Variations in fermentation methods, such as wet, dry, anaerobic, and carbonic, have different effects on the flavor characteristics of coffee. The success of fermentation is highly dependent on technical factors, including process duration, temperature, pH, oxygen availability, and the use of selected starter cultures. Inoculation with certain microbes, such as Saccharomyces cerevisiae or Lactobacillus plantarum, has been shown to improve flavor consistency while enriching sensory complexity. Thus, fermentation plays an important role in creating a more appealing flavor profile and increasing the competitiveness of Robusta coffee in the international market.