Exploring the use of Saccharomyces cerevisiae commercial strain and Saccharomycodes ludwigii natural isolate for grape marc fermentation to improve sensory properties of spirits

In Mediterranean countries the most diffuse practice to obtain the valorization of grape marc, the main by-product from winemaking, is the production of spirits. During this process, marc storage for sugar fermentation represents a crucial step, since side-fermentations leading to off-flavours production can very easily occur. In this study we evaluated the effect of the addition of two yeast strains, inoculated separately at the beginning of the storage period, into marcs from two Italian grape varieties with the aim to control the development of autochthonous microbiota and to improve spirit quality. The presence of the inoculated strains was monitored by means of PCR-based approaches. A commercial Saccharomyces cerevisiae strain, chosen as this species is notably the best ethanol producer, showed excellent ability to dominate the autochthonous microflora and to reduce off-flavours as demonstrated by chemical analysis and sensory evaluation. A Saccharomycodes ludwigii strain, chosen for increasing varietal compounds thus enhancing spirit aroma, showed a level of implantation not sufficient to assure a clear beneficial effect on quality. The implantation level of this strain was affected by S. cerevisiae competition since the highest level was found in grape marc with lower sugar content, where indigenous S. cerevisiae were less persistent.