Effect of pure and mixed cultures of the main wine yeast species on grape must fermentations

Mixed inoculation of non-Saccharomyces yeasts and S. cerevisiae is of interest for the wine industry for technological and sensory reasons. We have analysed how mixed inocula of the main non-Saccharomyces yeasts and S. cerevisiae affect fermentation performance, nitrogen consumption and volatile compound production in a natural Macabeo grape must. Sterile must was fermented in triplicates and under the following six conditions: three pure cultures of S. cerevisiae, Hanseniaspora uvarum and Candida zemplinina and the mixtures of H. uvarum:S. cerevisiae (90:10), C. zemplinina:S. cerevisiae (90:10) and H. uvarum:C. zemplinina:S. cerevisiae (45:45:10). The presence of non-Saccharomyces yeasts slowed down the fermentations and produced higher levels of glycerol and acetic acid. Only the pure H. uvarum fermentations were unable to finish. Mixed fermentations consumed more of the available amino acids and were more complex and thus better able to synthesise volatile compounds. However, the amount of acetic acid was well above the admissible levels and compromises the immediate application of mixed cultures.