Microbial diversity associated with spontaneous coffee bean fermentation process and specialty coffee production in northern Colombia.

Coffee fermentation involves the action of microorganisms, whose metabolism has a significant influence on the composition of the beans and, consequently, on the beverage's sensory characteristics. In this study, the microbial diversity during the wet fermentation of Coffea arabica L. in the Sierra Nevada of Santa Marta (SNSM) in Colombia was explored by high-throughput sequencing and the resulting cup quality through the standards of the Specialty Coffee Association. The taxonomic assignment of sequence reads showed a high microbial diversity comprised of 695 bacterial and 156 fungal genera. The microbial community was dominated by the Lactic Acid Bacteria (LAB) Leuconostoc, the yeast Kazachstania, and the Acetic Acid Bacteria (AAB) Acetobacter. Co-occurrence relationships suggested synergistic patterns between populations of LAB-AAB, yeasts-AAB, Leuconostoc-Prevotella, LAB-ABB-Selenomonas, and yeasts-fungi-nonLAB-nonAAB, which may result in the production of metabolites that positively impact the sensory attributes of coffee. The beverages produced were classified as specialty coffees, and their score was positively influenced by the fungal richness and the abundance of unclassified Lactobacillales, Pichia, and Pseudomonas. The findings show the richness and microbial diversity of the SNSM and serve as input for future research such as the analysis of microbial-derived metabolites and the establishment of starter cultures in coffee processing that guarantee the generation of high-quality beverages, the standardization of processes, the reduction of economic losses, and the production of value-added products that allow taking advantage of specialty coffee market.

Following Coffee Production from Cherries to Cup: Microbiological and Metabolomic Analysis of Wet Processing of Coffea arabica.

A cup of coffee is the final product of a complex chain of operations. Wet postharvest processing of coffee is one of these operations, which involves a fermentation that inevitably has to be performed on-farm. During wet coffee processing, the interplay between microbial activities and endogenous bean metabolism results in a specific flavor precursor profile of the green coffee beans. Yet, how specific microbial communities and the changing chemical compositions of the beans determine the flavor of a cup of coffee remains underappreciated. Through a multiphasic approach, the establishment of the microbial communities, as well as their prevalence during wet processing of Coffea arabica, was followed at an experimental farm in Ecuador. Also, the metabolites produced by the microorganisms and those of the coffee bean metabolism were monitored to determine their influence on the green coffee bean metabolite profile over time. The results indicated that lactic acid bacteria were prevalent well before the onset of fermentation and that the fermentation duration entailed shifts in their communities. The fermentation duration also affected the compositions of the beans, so that longer-fermented coffee had more notes that are preferred by consumers. As a consequence, researchers and coffee growers should be aware that the flavor of a cup of coffee is determined before as well as during on-farm processing and that under the right conditions, longer fermentation times can be favorable, although the opposite is often believed.IMPORTANCE Coffee needs to undergo a long chain of events to transform from coffee cherries to a beverage. The coffee postharvest processing is one of the key phases that convert the freshly harvested cherries into green coffee beans before roasting and brewing. Among multiple existing processing methods, the wet processing has been usually applied for Arabica coffee and produces decent quality of both green coffee beans and the cup of coffee. In the present case study, wet processing was followed by a multiphasic approach through both microbiological and metabolomic analyses. The impacts of each processing step, especially the fermentation duration, were studied in detail. Distinct changes in microbial ecosystems, processing waters, coffee beans, and sensory quality of the brews were found. Thus, through fine-tuning of the parameters in each step, the microbial diversity and endogenous bean metabolism can be altered during coffee postharvest processing and hence provide potential to improve coffee quality.

Microbial ecology and starter culture technology in coffee processing.

Coffee has been for decades the most commercialized food product and most widely consumed beverage in the world, with over 600 billion cups served per year. Before coffee cherries can be traded and processed into a final industrial product, they have to undergo postharvest processing on farms, which have a direct impact on the cost and quality of a coffee. Three different methods can be used for transforming the coffee cherries into beans, known as wet, dry, and semi-dry methods. In all these processing methods, a spontaneous fermentation is carried out in order to eliminate any mucilage still stuck to the beans and helps improve beverage flavor by microbial metabolites. The microorganisms responsible for the fermentation (e.g., yeasts and lactic acid bacteria) can play a number of roles, such as degradation of mucilage (pectinolytic activity), inhibition of mycotoxin-producing fungi growth, and production of flavor-active components. The use of starter cultures (mainly yeast strains) has emerged in recent years as a promising alternative to control the fermentation process and to promote quality development of coffee product. However, scarce information is still available about the effects of controlled starter cultures in coffee fermentation performance and bean quality, making it impossible to use this technology in actual field conditions. A broader knowledge about the ecology, biochemistry, and molecular biology could facilitate the understanding and application of starter cultures for coffee fermentation process. This review provides a comprehensive coverage of these issues, while pointing out new directions for exploiting starter cultures in coffee processing.

Evaluation of the composition effect of harvested coffee in the organoleptic properties of coffee drink / Evaluación del efecto de la composición del café cosechado en las propiedades organolépticas de la bebida de café

Background: The current flourishing of the specialty coffee market has motivated the development of this research on the basis that the harvested coffee fruits are a determining factor in drink quality. Objectives: The aim of this study was to evaluate the effect of the composition of harvested coffee (Coffea arabica L.) regarding the organoleptic quality of the coffee drink for the varieties Caturra and Colombia. Methods: Treatments for the assessed varieties were defined with different percentage compositions of coffee fruits M1 (100R), M2 (80R, 13OV, 7SR), M3 (60R, 26OV, 12SR, 2UR) and the control M4, which included fruits in different ripening stages, ripe (R), overripe (OV), semi-ripe (SR) and unripe (UR), in different proportions in experimental units of 10 kg of harvested coffee. The experimental design envisaged 3 rounds (repetitions) of harvest. The harvested coffee was classified manually according to its ripening stage using a previously developed scale based on colorimetry and recording the degrees Brix of 50 fruits in each ripening stage. The standardized wet processing method was carried out; a Q Grader cupping panel of five members was used for the sensory analysis of the coffee drink. Results: The results showed that for the variety Caturra statistical differences in cup quality between treatments were not found, whereas for the variety Colombia, treatments M1 and M3 showed similar behavior, with statistically significant differences regarding M2 and M4. Finally, the mathematical modeling obtained to predict the cup score depending on the coffee ripening stages composition, counted with coefficients of determination R2 of 0.946 and 0.852 with an error of 1.40 and 1.03% for the varieties Caturra and Colombia, respectively. Conclusions: The model developed with fuzzy logic and validated with information from other farms, presented an error of less than 2% in the estimation of the cup as a function of the ripening stages composition of the coffee varieties Caturra and Colombia.

Antecedentes: El progreso en el mercado de los cafés especiales, ha motivado el desarrollo de la presente investigación tomando como base que los frutos de café cosechados son un factor determinante en la calidad de la bebida. Objetivo: El objetivo del estudio fue la evaluación del efecto de la composición del café (Coffea arabica L.) cosechado respecto a la calidad organoléptica de la bebida para las variedades Caturra y Colombia. Métodos:, se definieron los tratamientos (composiciones en porcentaje) de café cereza M1 (100M), M2 (80M, 13SM, 7P), M3 (60M, 26SM, 12P, 2V) y testigo M4, las cuales contemplan para los estados de maduración maduro (M), sobremaduro (SM), pintón (P) y verde (V) en proporciones diferentes en unidades experimentales de 10 kg de café cereza. El diseño experimental contempló 3 pases (replicas) de cosecha. Una vez cosechado al café se realizó la clasificación manual de los estados de maduración con ayuda de una escala previamente elaborada, así como la verificación objetiva por colorimetría y el registro de los grados Brix para 50 frutos en cada estado de maduración. Se realizó un proceso de beneficio húmedo estandarizado; se utilizó un panel de catación Q Grader de cinco integrantes para el análisis sensorial de la bebida. Un análisis de varianza fue empleado para comparar los resultados y se usó lógica difusa para elaborar un modelo matemático predictivo de la calidad en taza en las dos variedades. Resultados: Los resultados mostraron que para la variedad Caturra no se encontraron diferencias estadísticas de calidad en taza entre los tratamientos, mientras que para variedad Colombia los tratamientos M1 y M3 presentaron igual efecto con diferencias estadísticas significativas respecto a M2 y M4. Finalmente, el modelamiento matemático obtenido para predecir la puntuación de la taza en función de la composición de los estados de maduración del café, contó con coeficientes de determinación R2 de 0,946 y 0,852 con errores de 1,40 y 1,03% en variedad Caturra y variedad Colombia, respectivamente. Conclusiones: El modelo desarrollado con lógica difusa validado con información de otras fincas presentó un error menor al 2% en la estimación de la taza en función de la composición de los estados de maduración del café variedad Caturra y Colombia.

Isolation, selection and evaluation of yeasts for use in fermentation of coffee beans by the wet process.

During wet processing of coffee, the ripe cherries are pulped, then fermented and dried. This study reports an experimental approach for target identification and selection of indigenous coffee yeasts and their potential use as starter cultures during the fermentation step of wet processing. A total of 144 yeast isolates originating from spontaneously fermenting coffee beans were identified by molecular approaches and screened for their capacity to grow under coffee-associated stress conditions. According to ITS-rRNA gene sequencing, Pichia fermentans and Pichia kluyveri were the most frequent isolates, followed by Candida Candida glabrata, quercitrusa, Saccharomyces sp., Pichia guilliermondii, Pichia caribbica and Hanseniaspora opuntiae. Nine stress-tolerant yeast strains were evaluated for their ability to produce aromatic compounds in a coffee pulp simulation medium and for their pectinolytic activity. P. fermentans YC5.2 produced the highest concentrations of flavor-active ester compounds (viz., ethyl acetate and isoamyl acetate), while Saccharomyces sp. YC9.15 was the best pectinase-producing strain. The potential impact of these selected yeast strains to promote flavor development in coffee beverages was investigated for inoculating coffee beans during wet fermentation trials at laboratory scale. Inoculation of a single culture of P. fermentans YC5.2 and co-culture of P. fermentans YC5.2 and Saccharomyces sp. YC9.15 enhanced significantly the formation of volatile aroma compounds during the fermentation process compared to un-inoculated control. The sensory analysis indicated that the flavor of coffee beverages was influenced by the starter cultures, being rated as having the higher sensory scores for fruity, buttery and fermented aroma. This demonstrates a complementary role of yeasts associated with coffee quality through the synthesis of yeast-specific volatile constituents. The yeast strains P. fermentans YC5.2 and Saccharomyces sp. YC9.15 have a great potential for use as starter cultures in wet processing of coffee and may possibly help to control and standardize the fermentation process and produce coffee beverages with novel and desirable flavor profiles.