Influenza del ceppo di lievito sui principali componenti volatili della grappa

"Influence of yeast strain on the main volatile components of Grappa" 

As is well known, yeast strains can strongly affect the fermentation process of any sugary material, not only as regards ethanol production but also, and above all, the development of secondary products like higher alcohols, esters, aldehydes and acids that seem to be mainly responsible for the aromatic characteristics of the finished product. In the case of Grappa, grape marcs collected from cellars are usually amassed at the distillery (in underground or above ground silos with a capacity of several dozen tons); especially with products of particular value (e.g. monovarietal grappas, etc.), specific measures are planned to prevent the mass from fermenting anomalously or to prevent bacterial contamination, which may irreparably alter quality. In the latter case grape marcs are divided into small batches and placed in different cylindrical or parallelepiped containers or even in plastic bags, where the transformation of sugars into ethanol is allowed to take place. As the grapes own microbial population is not considered optimal for the technological process, some producers are now considering the possibility of inoculating selected yeasts into the grape marc mass. The purpose of this investigation was to study the influence of some selected yeast strains as fermentation starters of virgin grape marcs destined to grappa production. Five selected yeast strains were used, from the Diproval collection (Bologna University), characterized by a different production of higher alcohols. The five groups of inoculated grape marcs, in addition to a control group in which only the indigenous yeasts were active, were first made to ferment in plastic cylindrical containers and then distilled using a discontinuous steam system. The results obtained from a gaschromatographic analysis of the water-alcohol slurry and full alcohol content intermediates were compared with the results of an organoleptic assessment carried out on grappas obtained after diluting the distillate to 40% alcohol by volume.