Effects of Mixing Ratio and Mixed Culture Fermentation on the Quality of Fuji-Merlot Wine

In order to improve the aroma and sensory quality of Fuji-Merlot wine, the mixing ratio between Fuji apple and Merlot grape juices was optimized and the mixed fruit juice was inoculated with non-Saccharomyces yeast and S. cerevisiae for mixed culture fermentation. The physicochemical indexes, color parameters and volatile aroma compounds of wine samples were determined, and the sensory scores were calculated using the fuzzy mathematical sensory evaluation method. The results showed that the mixing between grape and apple juices had a significant effect on the color saturation (C^*) and volatile components of apple-grape wine. Notably, the wine made from a 50:50 (V/V) mixture of apple and grape juices were characterized by bright color (luminosity (L^*) value of 76.24, red-green (a^*)) of 31.24, and C^* of 2.58) and high levels of volatile compounds including trans-nerolidol, β-damascenone, ethyl caproate, ethyl caprylate, and ethyl phenyl acetate. Non-Saccharomyces yeast had an insignificant effect on the color parameters of the wine. The wine fermented with a mixed culture of Torulaspora delbrueckii and S. cerevisiae had the largest number of volatile compounds (63) and significantly higher mass concentrations of isoamyl acetate, ethyl acetate, ethyl hexanoate, ethyl caprylate, phenethyl alcohol, 1-hexanol, and 1-heptanol than did pure S. cerevisiae fermentation and the other mixed culture fermentations. In addition, the wine had enhanced floral and fruity aromas with a sensory score of 7.6055. In conclusion, the apple-grape wine co-fermented by T. delbrueckii and S. cerevisiae was superior to apple wine fermented by S. cerevisiae in terms of sensory quality.