Enological potential and application of Metschnikowia pulcherrima in Vidal blanc icewine fermentation

Metschnikowia pulcherrima has been studied and applied in winemaking in recent years, but its application in icewine fermentation has rarely been reported. In this study, the tolerance and β-glucosidase activities of indigenous M. pulcherrima strain were first detected. The results show that, except for a relatively low tolerance to ethanol [limited to 4% (v/v)], the other tolerance is good to the fermentation of icewine; the cell wall-bound and extracellular β-glucosidase activities of <i>M. pulcherrima</i> strain were 35.93 nmol/mL (1.28 U) and 14.31 nmol/mL (0.42 U), respectively. M. pulcherrima and <i>Saccharomyces cerevisiae</i> (commercial and indigenous) strains were sequentially inoculated for icewine fermentations; meanwhile, pure S. cerevisiae fermentations were used as the control. The results showed that M. pulcherrima was completely replaced by S. cerevisiae in the middle and late stages of mixed culture fermentations of icewine. Compared with the icewine fermented with pure S. cerevisiae, the concentration of acetic acid and ethanol was lower, and the concentration of glycerol was higher in the mixed culture fermented icewines. After inoculation with M. pulcherrima, the levels of several important volatile compounds increased significantly, including β-damascenone, trans-rose oxide, isobutanol, isoamyl acetate, isobutyl acetate, and some ethyl esters (ethyl acetate, ethyl caprylate, ethyl caprate, ethyl nonanoate, ethyl hexanoate, and ethyl 9-decenoate). The pleasant fruity and flowery characteristics of mixed-fermentation icewine was intensified.