Effects of grape marcs acidification treatment on the evolution of indigenous yeast populations during the production of grappa

Aims: Grappa is a typical Italian product obtained from the distillation of grape marcs, the main by-product of grape crushing. One technological treatment frequently performed on marcs is their acidification, in order to contrast the development of unwanted spoilage bacteria during the storage period needed for alcoholic fermentation. A pilot-scale experiment was set-up to study the dynamics of yeast populations during a 30-day fermentation of acidified and nonacidified Prosecco grape pomace. Methods and Results: Saccharomyces cerevisiae population, examined after 4 and 15 days of storage by mitochondrial DNA-RFLP analysis, resulted considerably different at strain level upon acidification. In particular, although the number of different strains rescued appeared particularly high in both kind of marcs compared with what happens in must fermentation, in the acidified material such number tends to moderately decrease during storage. Conclusions: Results obtained evidence that the acidification treatment did not influence yeast population neither in terms of number of cells nor in terms of biodiversity at species level. Therefore, such treatment can be used in distillery without negatively influencing ethanol production. Significance and Impact of Study: Even though some data are available on the effects of technological treatments on the chemical composition of the distillate, no microbiological studies have been published so far on the consequence of these practices on composition, biodiversity and evolution of yeast population.