Final Examination for the Degree of MSc - Zheng Zhang

Examining Committee
Dr. Iris Joye, Chair
Dr. Loong-Tak Lim, Advisor
Dr. Donald Mercer, Advisory Committee Member
Dr. Massimo Marcone, Department Member

TITLE: DEVELOPMENT AND CHARACTERIZATION OF COFFEE BEVERAGES BY FERMENTATION OF COFFEE-SUGAR AQUEOUS SOLUTIONS USING DIFFERENT YEAST VARIETIES

ABSTRACT: Fermented coffee beverage is a relatively unexplored product with a limited information in the literature. This study investigated the feasibility of producing a novel low-alcoholic coffee beverage by fermenting instant coffee fortified with sucrose, i.e., coffee-sugar aqueous solutions (CSAS). Five different commercially available strains of Saccharomyces yeasts, including Safbrew wb-06, Safbrew wb-34/70 and SafAle US-05, Lalvin EC-1118 (EC-500), and SIHA Active Yeast 3 strain WET 136, were tested for the fermentation of the instant coffee solutions at different coffee concentrations for up to 7 d. Physiochemical properties (total soluble solid, reducing/total sugar, alcohol content, total acidity, and pH value) and volatile compounds of the products were measured. The fermented products were evaluated to determine the effect of yeast variety on sensory profiles. Safbrew wb-34/70 possessed the lowest alcohol/ester ratio of 10.67 while SafAle US-05 had the highest alcohol/ester ratio of 28.45. In the fermented samples, 64, 52, 53, 46, and 49 volatile components were detected in Safbrew wb-06, Safbrew wb-34/70, SafAle US-05, Lalvin EC-1118, and SIHA Active Yeast 3, respectively. Safbrew wb-34/70 was deemed to be the most optimal yeast candidate for this product on the basis of its good fermentation performance with the highest alcohol/ester ratio and its ability to retain typical and desirable coffee flavor characteristics. Further study was focused on controlling the alcohol content at less than 0.5% level by limiting the progression of fermentation, applying optimal yeast variety, and modifying CSAS concentrations from 0.5 to 2.5% w/w. Considering the fermentation rate, physicochemical and organoleptic properties, 2% CSAS was the most desirable formulation for the preparation of the fermented coffee beverage. In the final fermented products, the volatile compounds detected were mainly from the families of pyrazine, alcohol, acid, ester ketone, aldehyde, and furan.