The yeast Saccharomyces cerevisiae is the main species responsible for the process that involves the transformation of grape must into wine, with the initial nitrogen in the grape must being vital for it. One of the main problems in the wine industry is the deficiency of nitrogen sources in the grape must, leading to stuck or sluggish fermentations, and generating economic losses. In this scenario, an alternative is the isolation or generation of yeast strains with low nitrogen requirements for fermentation. In the present study, we carry out a genetic improvement program using as a base population a group of 70 strains isolated from winemaking environments mainly in Chile and Argentina (F₀), making from it a first and second filial generation (F₁ and F₂, respectively) based in different families and hybrids. It was found that the trait under study has a high heritability, obtaining in the F₂ population strains that consume a minor proportion of the nitrogen sources present in the must. Among these improved strains, strain “686” specially showed a marked drop in the nitrogen consumption, without losing fermentative performance, in synthetic grape must at laboratory level. When using this improved strain to produce wine from a natural grape must (supplemented and non-supplemented with ammonium) at pilot scale under wine cellar conditions, a similar fermentative capacity was obtained between this strain and a widely used commercial strain (EC1118). However, when fermented in a non-supplemented must, improved strain “686” showed the presence of a marked floral aroma absent for EC1118 strain, this difference being probably a direct consequence of its different pattern in amino acid consumption. The combination of the capacity of improved strain “686” to ferment without nitrogen addition and produce floral aromas may be of commercial interest for the wine industry.

The origin terroir provides distinctive characteristics for wines, in relation to soil, climate, oenological practices, etc. Hence, the characterization of each wine region by multiple aspects would allow differentiation of its wines. Several approaches at different scales have studied terroir microbiological fingerprints: from global microbiome analysis up to intraspecific Saccharomyces biodiversity. Mature grapes are the primary source of yeasts, and S. cerevisiae is a key wine fermentative species. Malbec is the emblematic Argentinean variety and is mainly cultivated in the “Zona Alta del Rio Mendoza” (ZARM). In this work, the diversity of S. cerevisiae grape populations was studied at three vintages in two Malbec vineyards of the ZARM, to evaluate their annual diversity and behavior in different vintages. Rarefaction of classical ecological indices was applied for a statistically adequate biodiversity analysis. A total of 654 S. cerevisiae isolates were differentiated by Interdelta-PCR. Each yeast grape population showed a unique composition of S. cerevisiae strains; however, a narrow genetic relationship was found in each vineyard. A slight increase in the initial diversity and a stabilization in the diversity of S. cerevisiae populations were confirmed. These results add to the discussion about the contribution of yeasts to the terroir microbiological concept, and its limitations and stability over the time.

Brettanomyces bruxellensis is recognized as the main spoilage yeast in red wines, producing volatile phenols that negatively impact wine quality. However, few studies have investigated strain diversity within wineries. Understanding the diversity and distribution of B. bruxellensis strains in different wines can provide insights into the origin and timing of contamination. This study aimed to evaluate the presence and diversity of B. bruxellensis biotypes during the production of four red wines in the same winery and to identify critical contamination stages. The analysis covered the entire process, from grape to six months of aging. B. bruxellensis yeasts were isolated and identified, and representative strains were typified by RAPD analysis. The results suggest that B. bruxellensis contamination did not originate from a single source. The grapes harbored low levels of B. bruxellensis, yet all wines were positive before barrel filling. This study demonstrates that winery equipment can serve as a vector for Brettanomyces introduction. Two critical contamination stages were identified: the shared use of equipment during fermentation, facilitating strain dissemination across wines, and the reuse of barrels, introducing new strains during aging. Additionally, some winery practices further promote B. bruxellensis spread and proliferation.

Problematic fermentations frequently drive economic losses and logistic problems in the winemaking industry. Previous studies have determined thermal conditions leading to problematic fermentations, selecting two contrasting yeast strains for further transcriptomic analysis. Saccharomyces cerevisiae SBB11 showed strong thermosensitivity towards heat shock, while S. cerevisiae PDM was found to be thermotolerant. The aim of this study was to select genes with significantly upregulated expression to be later used as biomarkers for early detection of sluggish fermentation associated with heat shock. Candidate genes were selected from previously obtained RNA-seq data. Alcoholic fermentations were conducted with 4 S. cerevisiae strains SBB11, PDM, M2 and ICV D21. Heat shocks on day 3 of alcoholic fermentation were applied at 36 and 40 °C for 16 h. S. cerevisiae cells were collected at different times after heat shock onset for qPCR analysis of candidate gene expression over time. Three genes showed promising results; SSA1, MGA1 and OPI10 significantly increased expression with respect to the control. The selected genes showed increased expression during the first 9 h post heat shock and are proposed for early detection of sluggish fermentations associated with heat shock.