Abstract
The use of non-Saccharomyces yeasts in sequential fermentations with S. cerevisiae has been proposed to improve the organoleptic characteristics involved in the quality of wine. The present study set out to select a non-Saccharomyces inoculum from the D.O.Ca. Rioja for use in winemaking. Strains included in the study belonged to Torulaspora delbrueckii, Lachancea thermotolerans, Metschnikowia pulcherrima, Zygosaccharomyces bailii, Williopsis pratensis, Debaryomyces hansenii, Pichia kluyveri, Sporidiobolus salmonicolor, Candida spp., Cryptococcus spp. and two mixed inocula of Lachancea thermotolerans-Torulaspora delbrueckii in a 30/70 ratio. In the first stage of the process, SO2 resistance and presence of enzymatic activities related to wine aroma and wine color and fining (esterase, esterase-lipase, lipase, leucine arylamidase, valine arylamidase, cystine arylamidase, β-glucosidase, pectinase, cellulose, xylanase and glucanase) were studied. In the later stages, selection criteria such as fermentative behavior, aroma compound production or influence on phenolic compounds were studied in laboratory scale vinifications. Taking into account the results obtained in the different stages of the process, a mixed inoculum of Lachancea thermotolerans-Torulaspora delbrueckii in a 30/70 ratio was finally selected. This inoculum stood out for its high implantation capacity, the production of compounds of interest such as glycerol and lactic acid and the consequent modulation of wine acidity. Given these characteristics, the selected inoculum is suitable for the production of quality wines.
Highlights
Spontaneous fermentations are complex microbial processes performed by the sequential action of indigenous non-Saccharomyces and Saccharomyces yeasts
In order to evaluate clonal diversity among the most representative non-Saccharomyces yeasts included in the study, genetic characterization was carried out in 71 isolates of five different species (T. delbrueckii, M. pulcherrima, L. thermotolerans, Z. bailii and W. pratensis)
This study shows the different steps carried out for the selection of a non-Saccharomyces yeast inoculum from the Rioja winegrowing region
Summary
Spontaneous fermentations are complex microbial processes performed by the sequential action of indigenous non-Saccharomyces and Saccharomyces yeasts. The high diversity of species involved in the process gives rise to wines with more complex profiles These fermentations are often associated with extended lag phases and long fermentation times, high residual sugar content and organoleptic defects [1]. These disadvantages, together with the lack of predictability of the process, have led winemakers to seek alternatives to spontaneous fermentations. The most extended practice in winemaking involves the inoculation of the must with selected S. cerevisiae strains in the form of active dry yeasts (ADY) This technique has some advantages, such as the rapid and complete fermentation of the must and great reproducibility of the final product [2]. This practice leads to less complexity and a certain standardization of the wines obtained as a consequence of the reduction of the diversity of the microbial populations involved in the fermentation [3,4]
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