Controlled fermentation of Arara coffee from cerrado mineiro

Abstract

Coffee is one of the most relevant products in Brazilian economy. Consumers have been looking for quality coffee with unique sensory characteristics, which has led to changes in post-harvest processing technologies. Fermentation is a potential tool for specialty coffees production. However, it still occurs in small quantities and has low reproducibility. The objective of this work was to study the influence of physical parameters (water addition and immature coffee fruit effect) and microbiological parameters (microorganisms’ inoculation) during the fermentation process on the sensorial quality and chemical composition of coffee. A literature review of coffee fermentation articles from the last 10 years was performed. The experimental section was carried out using whole fruits of Arabica coffee, cultivar Arara, from Fazenda Chuá of Grupo DB, in the city of Patos de Minas, submitted to fermentation in Self-Induced Anaerobic Fermentation (SIAF) in solid-state and submerged process. Two percentages of immature coffee fruits (0.3 and 11%) were studied during spontaneous fermentation. Also, the use of Saccharomyces cerevisiae and Bacillus amyloliquefaciens as inoculants were investigate. The experiments were evaluated regarding to effects on the physical-chemical composition of the coffee fruits (sugars, organic acids, ethanol, glycerol, moisture, protein, ash, titratable acidity, and lipids) and about the beverage sensorial quality evaluated according to the SCA protocol. According to the review it was found that post-harvest processing of coffee is no longer limited to wet, dry, and semi-dry, and the fermentation step can be determined by coffee fruit treatment, oxygen availability, water addition, and inoculum utilization. There is a migration from using processes in open environments to closed environments with induced anaerobiosis. However, it is not yet possible to define a single fermentative process capable to increase coffee quality or developing a specific sensory standard under any environmental condition. According to the experiments performed, the percentage of immature coffee fruits significantly altered the initial content of sugars (sucrose, glucose, and fructose), ash, and titratable acidity. The water addition during the fermentation process did not significantly influence moisture, protein, and citric, and propionic acid concentrations. The coffee fermented with 0.3% immature fruit showed high lactic acid production in the submerged process (67.44 mg/g), while in the solid-state process, they were higher for ethanol (42.84 mg/g) and glycerol (1.68 mg/g). Compared to the solid-state, the submerged process yielded coffees with lower concentrations of ethanol, glycerol, ash, lipids, succinic and acetic acids. Immature fruits present during fermentation in a percentage less than or equivalent to 11% may not negatively influence the sensorial quality of the coffee beverage. Water was able to modify the performance of the inoculum. Co-inoculated coffees obtained the highest sensorial scores in the submerged process, above 86 points. The type of process showed more influence in the chemical and sensorial analyses than the type of inoculum used. Coffees from the submerged process showed sensory descriptions of nutty, cocoa, and sweet, while the solid-state process produced coffee beverages with acidic, sour, and alcoholic characteristics.