Chemical and Sensory Profiles of Merlot Wines Produced by Sequential Inoculation of Metschnikowia pulcherrima or Meyerzyma guilliermondii

Technological application of autochthonous Meyerozyma guilliermndii cultures in Chardonnay

Using Chardonnay grape, the fermentation characteristics of sequential inoculation with M. guilliermondii and S. cerevisiae in the pilot fermentation process of dry white wine were examined. In this study, the physical and chemical indexes, color indexes, volatile aroma compound composition, and sensory indexes of 2 tons of samples at the end of alcoholic fermentation (AF) and malolactic fermentation (MLF) were analyzed. The results showed that the M. guilliermondii biomass in the treatment group (inoculated M. guilliermondii and S. cerevisiae sequentially) was always higher than 106 CFU/mL during AF, and the basic physicochemical indexes of samples met the requirements of the national standard GB/T15038-2006 (Wine). Also M. guilliermondii NM218 can significantly increase the color saturation of Chardonnay white wine. Regarding aromatic characteristics, the total alcohol, ester, and terpene contents of wine samples after mixed fermentation were higher than those of control group (only inoculated S. cerevisiae). Compared with control wine samples (only with S. cerevisiae), the treatment group had significantly increased ethyl caprylate, ethyl nonanoate, phenethyl acetate, and ethyl laurate contents, including n-heptanol, which can provide Chardonnay dry white wine a richer fruity fragrance. meanwhile, the sensory scores of wine samples were higher in the treatment group. In conclusion, mixed fermentation could boost the aroma quality and sensory pleasure of dry white wine, with the potential for industrial application.

Ethanol Reduction in Montepulciano Wine: Starmerella bombicola Sequential Fermentation at Pilot Scale Under Aeration Conditions

One of the most relevant challenges in winemaking is the increase in the alcohol content of wine, mainly due to climate change. The use of selected non-Saccharomyces yeasts in sequential fermentation with Saccharomyces cerevisiae is one of the effective strategies for dealing with this issue, even if it has been poorly confirmed at the winery level. This work evaluated the use of Starmerella bombicola and commercial S. cerevisiae strains in sequential fermentation at pilot scale in winery conditions to reduce the ethanol content and obtain a wine with enhanced aroma complexity. The results showed that the sequential S. bombicola/S. cerevisiae fermentation in aeration conditions (20 mL/L/min for the first three days) resulted in a reduction in ethanol of 0.80% (v/v) compared to pure S. cerevisiae fermentation. The aeration conditions of sequential fermentation did not affect the fermentation performance of yeasts. The winery conditions determined, in the sequential fermentation modalities, an enhancement of wild yeasts' presence. At the same time, the inoculation of S. bombicola determined an enhancement of glycerol and lactic acid, which positively influences the structure and body of the wine as well as specific aromatic notes. In winery conditions, better control of fermentation is needed to achieve potential ethanol reduction and favorable by-product formation using S. bombicola.

Integration of LC-HRMS and 1H NMR metabolomics data fusion approaches for classification of Amarone wine based on withering time and yeast strain

Two untargeted metabolomics approaches (LC-HRMS and 1H NMR) were combined to classify Amarone wines based on grape withering time and yeast strain. The study employed a multi-omics data integration approach, combining unsupervised data exploration (MCIA) and supervised statistical analysis (sPLS-DA). The results revealed that the multi-omics pseudo-eigenvalue space highlighted a limited correlation between the datasets (RV-score = 16.4%), suggesting the complementarity of the assays. Furthermore, the sPLS-DA models correctly classified wine samples according to both withering time and yeast strains, providing a much broader characterization of wine metabolome with respect to what was obtained from the individual techniques. Significant variations were notably observed in the accumulation of amino acids, monosaccharides, and polyphenolic compounds throughout the withering process, with a lower error rate in sample classification (7.52%). In conclusion, this strategy demonstrated a high capability to integrate large omics datasets and identify key metabolites able to discriminate wine samples based on their characteristics.

Bio-protection in oenology by Metschnikowia pulcherrima: from field results to scientific inquiry

Finding alternatives to the use of chemical inputs to preserve the sanitary and organoleptic quality of food and beverages is essential to meet public health requirements and consumer preferences. In oenology, numerous manufacturers already offer a diverse range of bio-protection yeasts to protect must against microbiological alterations and therefore limit or eliminate sulphites during winemaking. Bio-protection involves selecting non-Saccharomyces yeasts belonging to different genera and species to induce negative interactions with indigenous microorganisms, thereby limiting their development and their impact on the matrix. Although the effectiveness of bio-protection in the winemaking industry has been reported in numerous journals, the underlying mechanisms are not yet well understood. The aim of this review is to examine the current state of the art of field trials and laboratory studies that demonstrate the effects of using yeasts for bio-protection, as well as the interaction mechanisms that may be responsible for these effects. It focuses on the yeast Metschnikowia pulcherrima, particularly recommended for the bio-protection of grape musts.

Improving the Aromatic Profiles of Catarratto Wines: Impact of Metschnikowia pulcherrima and Glutathione-Rich Inactivated Yeasts

Catarratto is one of the most widely cultivated grape varieties in Sicily. It is an indigenous non-aromatic white grape variety. Despite its widespread use in winemaking, knowledge of the aroma and chemical and microbiological properties of Catarratto wines is quite limited. The influence of Metschnikowia pulcherrima combined with Saccharomyces cerevisiae on the aromatic expression of Catarratto wines was investigated with and without the addition of glutathione-rich inactivated yeast. The substance is a natural specific inactivated yeast with a guaranteed glutathione level used to limit oxidative processes. The aromatic profiles of the final wines were determined through analysis of the volatile organic compounds using a solid-phase microextraction technique that identified 26 aromatic compounds. The addition of M. pulcherrima in combination with the natural antioxidant undoubtedly increased the aromatic complexity of the wines. Dodecanal was exclusively detected in the wines processed with glutathione-rich inactivated yeasts. Furthermore, the presence of this natural antioxidant increased the concentration of six esters above the perception threshold. Sensory analysis was also performed with a panel of trained judges who confirmed the aromatic differences among the wines. These results suggest the suitability of glutathione-rich inactivated yeasts for determining the oxidative stability of Catarratto wines, thus preserving its aromatic compounds and colour.

Application of Cool Fermentation Temperatures to Encourage Non-Saccharomyces Yeasts to Yield Lower Ethanol Concentrations in Wines

Application of cool temperatures were studied to encourage Metschnikowia pulcherrima P01A016 and Meyerozyma guilliermondii P40D002 prior inoculation of Saccharomyces cerevisiae D254 to lower ultimate ethanol concentrations achieved. Merlot grape must was distributed into 300 L temperature-controlled tanks and inoculated with non-Saccharomyces yeasts three days before S. cerevisiae. For control fermentations, S. cerevisiae was inoculated with maximum temperatures set to 25 °C (temperature regime I) while those with Mt. pulcherrima or My. guilliermondii were initially set to 15 °C (temperature regime II) or 17.5 °C (temperature regime III) before increasing to 25 °C after adding S. cerevisiae. Once fermentations achieved dryness (≤2 g/L residual sugar), wines were bottled and stored for six months at 7 °C before sensory analysis. Ethanol reduction by Mt. pulcherrima was not observed in wines fermented under II but was by III (0.8% v/v). In contrast, musts inoculated with My. guilliermondii yielded wines with ethanol concentrations lowered by 0.3% (II) or 0.4% v/v (III). Sensory panelists found wines with Mt. pulcherrima to express lower sensory scores for ‘hotness’, ‘bitterness’, and ‘ethanol’ flavor with fewer differences noted for My. guilliermondii. Reducing final ethanol concentrations of Merlot wines were achieved by Mt. pulcherrima or My. guilliermondii using cooler initial fermentation temperatures without adversely affecting final wine quality.

Biotechnological Approaches to Lowering the Ethanol Yield during Wine Fermentation

One of the most prominent consequences of global climate warming for the wine industry is a clear increase of the sugar content in grapes, and thus the alcohol level in wines. Among the several approaches to address this important issue, this review focuses on biotechnological solutions, mostly relying on the selection and improvement of wine yeast strains for reduced ethanol yields. Other possibilities are also presented. Researchers are resorting to both S. cerevisiae and alternative wine yeast species for the lowering of alcohol yields. In addition to the use of selected strains under more or less standard fermentation conditions, aerobic fermentation is increasingly being explored for this purpose. Genetic improvement is also playing a role in the development of biotechnological tools to counter the increase in the wine alcohol levels. The use of recombinant wine yeasts is restricted to research, but its contribution to the advancement of the field is still relevant. Furthermore, genetic improvement by non-GMO approaches is providing some interesting results, and will probably result in the development of commercial yeast strains with a lower alcohol yield in the near future. The optimization of fermentation processes using natural isolates is, anyway, the most probable source of advancement in the short term for the production of wines with lower alcohol contents.