Improvement characteristics of semi-dry coffee fermentation with starter yeasts

Abstract

Brazil is known worldwide for being one of the highest producers and exporters of coffee. Before beverage production, beans go through different processing methods: dry, semi-dry and wet, choosing one will depend on the producer or farmer. During the process, cherries or beans are fermented spontaneously while drying until reaching approximately 11% of moisture. Sometimes starter cultures are used to help fermentation that results in special coffees. Natural organisms of coffee involve yeasts, filamentous fungi, aerobic bacteria and facultative bacteria that consume sugars, produce acids that subsequently low pH. Coffees of high qualities have characteristic aromas and flavors and most have beneficial health compounds. This work aimed at evaluating the behavior of three-yeast previously tested starters (Saccharomyces cerevisiae CCMA 0543, Candida parapsilosis CCMA 0544 and Torulaspora delbrueckii CCMA 0684) inoculated in coffee process via semi-dry method, implementing two inoculation methods: direct inoculation and bucket inoculation. Total population of yeast, lactic acid and mesophilic bacteria was evaluated by plating. Posteriorly, the population of starters was monitored by real-time polymerase chain reaction (qPCR). Metabolites consumed and produced during fermentation in both inoculation methods were evaluated using liquid chromatography (HPLC) and gas chromatography (GC-MS) for green and roasted beans. Finally, a cup test was carried out as sensorial analysis. As a result, plate counting showed that bucket method maintained a higher population of yeast, lactic acid and mesophilic bacteria at the end of fermentation (drying). Sucrose was consumed in all tested treatments. Citric and succinic acid were detected during all fermentation processes. After roasting, the average levels of chlorogenic acid were higher for the bucket method and the same for trigonelline and caffeine concentration, except for the T. delbrueckii CCMA0684 assay. Group of acids and alcohols in green beans and pyrazines and pyridines in roasted beans were the main volatile compounds. Scores from both inoculation methods in the cup test were above 80, proving that the inoculation had a positive effect and produced beverages of good quality.