Lucía Maribel Becerra

Criolla grape varieties are native South American cultivars that represent an important reservoir of genetic and microbiological diversity. This study aimed to investigate the oenological potential of Saccharomyces and non-Saccharomyces yeasts isolated from three criolla grape varieties in order to support the future design of wine starters. Yeasts were isolated at different fermentation stages from four vineyards in Mendoza, Argentina. A total of 485 isolates were recovered and molecularly identified, revealing 12 species belonging to eight genera. Saccharomyces cerevisiae, Hanseniaspora guilliermondii and Hanseniaspora uvarum were the dominant species. Isolates were screened for H₂S and acetic acid production, followed by physiological and enzymatic characterisation. Selected strains were further evaluated in small-scale fermentations to assess fermentative kinetics and metabolic performance. Significant variability was observed, particularly among non-Saccharomyces isolates, which generally exhibited lower ethanol yields and acetic acid production compared to S. cerevisiae. Several isolates of H. guilliermondii showed balanced fermentative behaviour and favourable metabolic and enzymatic profiles. Through the applied selection strategy, twelve strains emerged as promising wine starter candidates. These isolates combined a low production of undesirable metabolites, relevant enzymatic activities, and favourable fermentative performance. Overall, the results highlight the oenological potential of autochthonous yeasts as a resource for innovative winemaking strategies.

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.

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.