The constant demand of the consumer market for high-quality coffees has led to the need to understand the total microbiotic environment of dry or naturally processed coffee, and to determine the role of these microorganisms in the organoleptic characteristics of the final beverage.
Studies on natural coffee microbes always emphasize filamentous fungi isolation and identification, but the predominant microorganisms during the fermentation and drying period are bacteria and yeasts.
Traditionally, naturally processed coffees originate from stripping the berries at various stages of ripeness.
In this study, the coffee berries were harvested at a single stage of ripeness (red cherry) and placed on the fermentation and drying platform.
This methodology was different from that used in other studies already published and allowed us to verify the existence of the succession of microbial groups.
Microbial succession was established with the predominance of bacteria at the initial fermentation stages and with the presence of filamentous fungi and yeasts throughout the entire process on fermentation days when the aw was around 0.8. Gram-positive sporulating bacteria were isolated throughout the fermentation and storage period, perhaps because of spore formation under adverse conditions.
Filamentous fungi were also detected throughout the process, possibly due to isolation of spores present on the surface of cherries because there was no visible mycelia colonization.
Gram-negative bacteria predominated in the initial fermentation phases (up to the 12th day—19% moisture) because they are less resistant to low moisture content than Gram-positive bacteria.
D. hansenii and Pichia were the most frequent among the yeast isolates, but were still present in smaller populations than bacteria and fungi species. However, the yeasts identified in this study have been reported to inhibit of filamentous fungi mycelial growth and could thus be potentially used for biocontrol of filamentous fungi growth.
This inhibition of fungal development may be of particular importance in coffee regions where the atmospheric conditions are adverse during natural coffee fermentation (high humidity, no sunshine and high rainfall).