Dominance of S. cerevisiae Commercial Starter Strains during Greco di Tufo and Aglianico Wine Fermentations and Evaluation of Oenological Performances of Some Indigenous/Residential Strains

Management of in-Amphora "Trebbiano Toscano" Wine Production: Selection of Indigenous Saccharomyces cerevisiae Strains and Influence on the Phenolic and Sensory Profile

The use of earthenware amphorae in winemaking can give wines unique attributes enhancing their typicity. Therefore, in this study, spontaneous and inoculated in-amphora fermentations of Trebbiano Toscano grape must were monitored to assess the Saccharomyces cerevisiae strains occurring in each fermentation as well as the chemical characteristics of the wines. Strain typing via Interdelta analyses pointed out that the commercial starters did not dominate, showing 24% and 13% implantation percentages, and that 20 indigenous strains were present at different percentages, ranging from 2 to 20%, in inoculated and spontaneous fermentations. The assessment of the technical characteristics of the indigenous strains via fermentations at lab and pilot scale (20 L amphorae) and the sensory analysis of the experimental wines allowed for the selection of two indigenous strains to be used as starter cultures in comparison to a commercial strain in 300-L-amphorae vinifications in the cellar. The observed fermentative performances and sensory analysis of the experimental wines highlighted that one indigenous S. cerevisiae strain dominated the process and conferred distinctive sensory characteristics to the Trebbiano Toscano wine, demonstrating its effectiveness in managing the in-amphora fermentations. In addition, the results demonstrated the ability of amphorae to protect the polyphenolic compounds from oxidation during wine ageing. Indeed, the concentration of both hydroxycinnamic acids and flavonols decreased, with an average reduction of 30% and 14%, respectively, while hydroxybenzoic acids remained unchanged.

Hybridization and spore dissection of native wine yeasts for improvement of ethanol resistance and osmotolerance

Global warming has a significant impact on different viticultural parameters, including grape maturation. An increment of photosynthetic activity generates a rapid accumulation of sugars in the berry, followed by a dehydration process which leads to a higher concentration of soluble solids. This effect is exacerbated by current viticultural practices which favor the harvest of very mature grapes to obtain wines with sweet tannins. Considering the initial hyperosmotic stress conditions and the high ethanol concentration of the produced wine, fermentation of grape musts with high sugar content could be problematic for yeast starters. In the present study, we were able to obtain by classical hybridization and spore dissection methods one hybrid and one monosporic wine yeast strain with a combined ethanol and osmotolerant phenotype. The improved yeasts were tested in vinification trials with high sugar concentration and displayed excellent fermentation performance. Importantly, the obtained wines also showed good organoleptic properties during sensory analysis. Based on our results, we believed our improved hybrid and monosporic strains can be considered good alternatives to be used as yeast starters for fermentations with high sugar content.

Survey of Inoculated Commercial Saccharomyces cerevisiae in Winery-Based Trials

Wine production has developed from spontaneous to controlled fermentations using commercial active dry yeasts (ADY). In this study, S. cerevisiae commercial ADY were tested, and yeast community dynamics were monitored at different fermentation stages in three winery-based trials with volumes ranging from 60 L to 250 hL. The differentiation of S. cerevisiae strains was achieved using microsatellite markers. In Experiment 1, results showed that both ADY strains revealed similar profiles, despite being described by the producer as having different properties. In Experiment 2, higher genetic diversity was detected when co-inoculation was tested, while in sequential inoculation, the initial ADY seemed to dominate throughout all fermentation. Pilot-scale red wine fermentations were performed in Experiment 3, where one single ADY strain was tested along with different oenological additives. Surprisingly, these trials showed an increase in distinct profiles towards the end of fermentation, indicating that the dominance of the ADY was lower than in the blank modality. The use of ADY is envisaged to promote a controlled and efficient alcoholic fermentation, and their purchase represents an important cost for wineries. Therefore, it is most relevant to survey commercial ADY during wine fermentation to understand if their use is effective.

Selection of Indigenous Saccharomyces cerevisiae Strains and Exploitation of a Pilot-Plant to Produce Fresh Yeast Starter Cultures in a Winery

The inoculation of grape juice with Saccharomyces cerevisiae strains selected from indigenous yeast populations can be a suitable tool to control alcoholic fermentation, contributing to producing wines with typical flavor and aroma and, hence, the demand for native starter cultures is increasing. However, since low amounts of indigenous yeast biomasses are usually required for local winemaking, the industrial production of these yeasts can be expensive. Therefore, in this study, after selecting an indigenous S. cerevisiae strain based on relevant oenological and technological features, a pilot-plant for easy and rapid production of fresh yeast biomass directly in a winery located in Tuscany, was exploited. The selected yeast strain was used as a starter to carry out 25 and 100 hL fermentations and its enological performance was compared with that of the commercial starter normally used in the winery. Chemical and sensory analysis of the resulting wines showed that they differentiated according to the used yeast strain, with the wines produced by the indigenous S. cerevisiae strain being characterized by a distinctive aromatic and sensory profile. In conclusion, the pilot-plant effectively resulted in producing fresh yeast starter cultures in the winery to be successfully used to carry out alcoholic fermentations.