Chemical and sensory evaluation of Merlot wines fermented by mixed cultures of Lachancea thermotolerans and Saccharomyces cerevisiae

Mestrado em Engenharia de Viticultura e Enologia (Double Degree) / Instituto Superior de Agronomia. Universidade de Lisboa / Faculdade de Ciências. Universidade do Porto

Topic position & objectives: Excessive ethanol and insufficient acidity are the key challenges in winemaking considering the trends in increasing sugar and decreasing acidity in grapes/musts due to global warming. The species Lachancea thermotolerans yeast has been researched recently due to its high yields of lactic acid and low yields of ethanol. The present work tested the performance of five strains of L. thermotolerans in mixed fermentation with S. cerevisiae. Methods: Vitis vinifera L. cv. Merlot grapes were fermented with mixed cultures of L. thermotolerans and S. cerevisiae in sequential and co-inoculation regimes, alongside a pure culture S. cerevisiae and an un-inoculated treatment set as controls. Yeast growth was monitored by plate counts, fermentation metabolites were analyzed by High Performance Liquid Cromatography (HPLC), colorimetric properties by CIELab coordinates and sensory analysis was conducted by RATA. Results: Tested yeast treatments affected wine profiles. pH dropped drastically, especially in the sequential inoculations. Ethanol content was lower in sequential inoculations compared to pure culture S. cerevisiae. Sequential inoculations also had significantly higher titratable acidity, explained by high level of lactic acid. Low levels of acetic acid (mean: 0.35 g/L) were confirmed in all the cases. CIELab showed visible differences (ΔE*> 2) between all the treatments, and sensory analysis confirmed the differences observed in the chemical profiles of wines, in terms of acidity and alcohol. Main conclusions: L. thermotolerans yeast has enological advantages and may be used in mixed cultures with S. cerevisiae. The five different strains showed different behavior regarding both the fermentation kinetic and the yield of metabolites produced. Furthermore, the S. cerevisiae inoculation timing influenced these aspects. The appropriate strains and inoculation regimes can therefore be targeted by winemakers to manage the characteristics of wines

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