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.

In the field of winemaking, malolactic fermentation is a key aspect in obtaining high quality wines. Unfortunately, in some oenological contexts effective evolution does not take place because of the occurrence of certain limiting factors for malolactic bacteria in wine. Simultaneous alcoholic and malolactic fermentation in grape must is a promising alternative that promotes the survival of bacteria, due to the absence of certain limiting factors such as ethanol or other toxic substances produced by yeasts in the native grape must. The risk of wine depreciation due to the spoilage activity of malolactic bacteria can be reduced by using selected strains of Oenococcus oeni, with proven behaviour in terms of malolactic fermentation occurring in the presence of sugars. In this work we compared the activity of a strain of Oenococcus oeni in malolactic fermentation of a Chardonnay grape must, using different winemaking protocols characterised by sequential or simultaneous inoculums of microbial starters. The results are discussed both in terms of fermentative behaviour and the quality of the wines obtained, with careful analysis of the main chemical parameters of the wines and of 47 different volatile compounds, giving an exhaustive overview of the opportunities and the risks related to different wine fermentation strategies.