ndeed, different yeast strains in co-cultures can have positive or negative interactions regarding different analytical compounds. In this regard, two different metabolic mechanisms shown by yeast in mixed cultures can be distinguished: simple additive effects, or specific metabolic interactions. Indeed, in some cases the aromatic profile of the wine is influenced by the simple addition of metabolites produced by each yeast from partial consumption of carbon or nitrogen sources, or by a specific metabolic activity (i.e., enzymatic activity) [34]. In this case, the persistence of the specific yeast in the mixed fermentation determines the level of metabolite production or the metabolic activity. For example, the enhancement of glycerol levels and total acidity shown by mixed fermentation with Starmerella bombicola (formerly Candida stellata)/S. cerevisiae and L. thermotolerans (formerly Kluyveromyces thermotolerans)/S. cerevisiae, respectively, are strictly related to the persistence and competitiveness of the non-Saccharomyces strains [12]. Also, the ethanol reduction can be affected by the simple metabolic activity of co-inoculation of non-Saccharomyces yeast. In this case, the overall ethanol reduction is due to the reduced alcoholic fermentation efficiency of the non-Saccharomyces co-inoculated strain 8, 9 and 10.