Chemical and microbiological assessment of early wine fermentation phase can predict yeast cell viability during post-fermentation process.

The management of post-fermentation phase is essential for the protection of wine oxidation. The prolonged contact of yeast lees and wine can help to limit this problem, although off-flavours can originate. It is known that some cellular components (mannoproteins, lipids, glutathione, etc.) released into the wine influence oxygen protection; however, still active cells could contribute to maintaining protection against oxidation. To date, in the literature there is a lack of data that evaluates cell viability, especially in the post-fermentation phase, particularly using methods different by plate count that identifies only a small part of the viable population. The aim of the work was to investigate the yeast viability of 12 wine Saccharomyces cerevisiae strains during 45 days after the fermentation in natural grape juice. The major fermentation parameters were measured at early phase (40 h) and at the end of the process, and were correlated with total and viable cells in the post-fermentation phase. Contrary to what has been observed in the literature, this work demonstrates that cell viability in the post-fermentation phase is very high and dependent on the yeast strain. A predictive model that can estimate viability in the post-fermentation phase, based on parameters measured at the early fermentation phase, was successfully set up. This approach can be adopted by wineries or winemakers as it uses fermentation data (sugar and nitrogen residues, ethanol and glycerol production, total cell count) obtained through simple chemical and microbiological analyses.