Assessing the Impact of Yeast Fermentation in Dry Processing on Coffee Quality from Coffea arabica cv. Caltimor, C. arabica cv. Bourbon and C. canephora cv. Robusta

Abstract

This study aims to investigate the influence of yeast fermentation and inoculation methods on the quality of coffee across 3 different coffee cultivars. Fermenting Sacchoromyces cerevisiae SafAle s-33 on Coffea arabica cv. Caltimor via bucket inoculation outperforms spray inoculation across all aspects including microbial cell adhesion, the chemical profile, reducing sugar content and sensory analysis conducted by a Q-grader. The PCA analysis revealed distinct profiles of organic acids and volatile compounds in roasted beans in yeast fermentation and natural fermentation of all 3 coffee varieties. Particularly, volatile compounds such 1-(4-Methoxyphenyl)octan-1-one, 8-Oxabicyclo[3.2.1]oct-6-en-3-one and 5,6-Dimethoxy-2-(2-hydroxyethyl-1-thio)-3 trimethylsilyl methyl-1,4-benzoquinone and, furfuryl ethyl ether and 5-methyl furfural were detected only in yeast fermented bean. The malic acid also contained a higher amount in roasted coffee beans from the yeast fermentation of all 3 coffee varieties than the natural fermentation. Those compounds present a notably positive influence on the sensory aspects of the coffee i.e. sweet caramel, dry fruit, vanilla and hazelnut-like flavors. In addition, roasted beans from the yeast fermentation of C. arabica cv. Caltimor and C. canephora cv. Robusta displayed higher sensory scores when compared to those from natural fermentation, conversely in C. arabica cv. Bourbon, beans from both yeast fermentation and natural fermentation displayed similar quality levels. Our study concluded that the commercial yeast strain within the beer and wine industry proved to be an alternative source for coffee fermentation. Nevertheless, the selection of the coffee variety plays a crucial role when utilizing S. cerevisiae SafAle s-33 as a starter.