Improvement characteristics of semi-dry coffee fermentation with starter yeasts

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