Hanseniaspora vineae (Hv) is a non-Saccharomyces yeast with unique metabolic features, making it appealing for wine production. However, Hv presents high nutritional requirements that may lead to slow fermentation. This study investigated the impact of sequential inoculation of Saccharomyces cerevisiae (Sc) in white winemaking at different time points (24, 48, 74, 100 and 200 h) during Hv fermentation and compared them to simultaneous inoculations. The 200 h protocol extended fermentation by an average of 13 days compared to pure Sc, decreasing with earlier sequential inoculation. Sc wines were richer in isoamyl acetate and ethyl hexanoate than Hv wines, with no significant differences among inoculation protocols. β-phenylethyl acetate was increased in Hv wines, particularly in the 24 h protocol. The 2-phenylethanol concentration was negatively correlated with the S. cerevisiae inoculation delay. Hv altered the wine aroma features, enhancing the compounds associated with rose-like scents. Reducing the Sc inoculation delay aligned Hv with industrial standards while maintaining increased β-phenylethyl acetate production. However, co-inoculation with Sc seems to better meet the Hv requirement without sacrificing the main aromatic features of Hv, demonstrating faster sugar depletion and higher acetate and ethyl ester contents, suggesting that co-inoculation yields a more modulable wine aroma profile.

In this work, Lachancea thermotolerans was exploited as a biological acidifier of Vino Santo di Gambellara, a traditional Italian wine made from long-dried grapes. The drying of grapes before winemaking is a traditional technique widely applied in Italy in the production of sweet wines, but in recent years, global warming reduces dramatically the acidity of grapes, causing microbial instability during drying and winemaking. The ability of L. thermotolerans to convert sugars in lactic acid was already applied in the acidification of red wines, but the peculiar features of dried grape (e.g., osmotic stress, lack of nutrients, presence of mould-derived toxic compounds during drying) impose specific tests. L. thermotolerans was employed in sequential fermentation in combination with a strain of Saccharomyces cerevisiae. Considering the lack of information about the nutritional requirement of the non-Saccharomyces yeast, three protocols of nitrogen supplementation (mineral, organic and organic at high dosage) were tested. Alcoholic fermentation experiments were followed by plate counts onto differential media to discriminate between the two yeast species and by chemical analysis. Moreover, a GC-MS-MS approach carried out a complete characterisation of the volatile profile of wines. Results evidenced a long permanence of L. thermotolerans during alcoholic fermentation, which remained over the 7 log units until the 14th day of fermentation. The nitrogen supplementation protocol influenced cell growth and fermentative activity. Inorganic nitrogen supplementations allowed the accomplishment of alcoholic fermentation and the maintenance of pH below 3.35, with respect to the control wine (made only by S. cerevisiae), which was over pH 3.50. L. thermotolerans also influenced the wine's volatile aroma profile. Statistical differences were found in the main families of the yeast-derived aroma: acetate, esters, lactates, fatty acids and C6 compounds.

Yeast derivatives (YDs) are commercial products obtained from yeast colonies grown in bioreactors then inactivated and dried. They are employed in winemaking to supply nitrogen (N), enhance yeast growth and remove unwanted compounds. Since glucose is the primary carbon and energy source for yeast growth, agricultural byproducts are commonly used in their production. Atypical aging (ATA) is a wine aroma defect arising from the oxidation of indole-3-acetic acid (IAA) to 2-aminoacetophenone (AAP). It entails the appearance of unpleasant odours as well as the rapid loss of varietal aromas. As IAA is one of the main plant hormones and YDs are often manufactured using material of plant origin, it can be assumed that AAP precursors are contained in those commercial formulations. If this is the case, the use of YDs could potentially increase the risk of obtaining ATA-tainted wines. To explore this hypothesis, 28 YDs were screened for the presence of AAP-related compounds, as well as their amino acidic content. Since several ATA precursors were detected, fermentation experiments were carried out in which different amounts of YD were added to different grape musts. Interestingly, depending on the nature of the commercial formulation, AAP development was observed to be either enhanced or diminished. More specifically, as well as concentration of AAP and precursors, the presence of cell walls within the YDs seemed to have an influence on the development of this defect. Furthermore, as diammonium phosphate (DAP) is also used to provide grape must with N, the effect of supplementing must with DAP was investigated. The addition of increasing doses of DAP did not significantly affect the accumulation of AAP. These results are very promising for both winemakers and YD producers, and they highlight the need for further research on the use of YDs in oenology.