Effects of Mixed Fermentation on the Aroma Compounds of ‘Italian Riesling’ Dry White Wine in Eastern Foothill of Helan Mountain

To study the effect of mixed fermentation of non-<i>Saccharomyces</i> strains and <i>Saccharomyces cerevisiae</i> on the aroma quality of ‘Italian Riesling’ wine in the eastern foothill of Helan Mountain and to determine the most optimum process of mixed fermentation, two selected non-<i>Saccharomyces</i> strains, including <i>Hanseniaspora uvarum</i> YUN268 and <i>Pichia fermentans</i> Z9Y-3, were inoculated with <i>Saccharomyces cerevisiae</i> in different proportions (10:1 or 1:1) and different stages (48 h in advance or simultaneously at the beginning) to ferment ‘Italian Riesling’ dry white wine. The oenological parameters and aroma indexes of the wine samples were evaluated. The results showed mixed fermentation can not only reduce the alcohol content of wine 0.24~0.71% vol but also increase the glycerol content to improve the taste of wine. The mixed fermentation effect of <i>Pichia fermentans</i> Z9Y-3 and <i>Saccharomyces cerevisiae</i> resulted in improvements, especially the high proportion (10:1) sequential inoculation and simultaneous inoculation of wine samples (WSP10 and WCP10), which not only produced more volatile aroma substances and glycerol content but also increased the total amount of ester substances by 49.4% and 56.5%, respectively, compared with the control. The sensory evaluation scores of WSP10 and WCP10 were significantly higher than the control (89.3 and 88.1 points, respectively). At the same time, it can also enhance the aroma of lemon, cream, almond, and others and increase the aroma complexity of wine. Therefore, these two methods of mixed fermentation inoculation are more suitable for the production of Italian Riesling wine in the eastern foothill of Helan Mountain. In conclusion, the mixed fermentation of <i>Pichia fermentans</i> Z9Y-3 and <i>Saccharomyces cerevisiae</i> 10:1 (simultaneous or sequential) inoculation is suitable for the production of Italian Riesling dry white wine in the eastern foothill of Helan Mountain.