Implementing principles of traditional concentrated grape must fermentation to the production of new generation balsamic vinegars. Starter selection and effectiveness.

In an effort to implement principles of traditional concentrated grape must fermentation to the production of new generation balsamic vinegars (BVs), the specific goals of the study were the isolation and molecular identification of the predominant yeasts in concentrated grape must (cv. Xinomavro), their technological characterization and the evaluation of the fermentative aptitude of the selected strains. Tolerance against 5-hydroxymethyl-furfural (HMF) and furfural, acetic acid and glucose concentration was examined by appropriate methods and tests. The enological characteristics studied were acetic acid and H2S production, foaming and flocculation ability and key enzymatic activity. PCR-RFLP analysis revealed only the presence of Saccharomyces cerevisiae and Hanseniaspora uvarum among the 14 predominant osmophilic yeast isolates. Tolerance to both HMF and furfural was found strain- and dose-dependent and was suggested as a critical factor in the pre-selection of yeast starters. The most tolerant yeasts to these stress factors, a S. cerevisiae and a non-Saccharomyces strains, showed satisfactory growth in the presence of high glucose and acetic acid content (up to 600 g/L and 2 % w/w, respectively) and desirable enological characteristics. Results from the comparative evaluation of the fermentative aptitude of these strains with a commercial wine strain highlighted that the isolates had glucophilic behaviour and ability to produce desirable amounts of ethanol (100-120 g/kg) in short time (~20 d). The key volatiles useful for varietal discrimination and differentiation between the BVs and the traditional ones were also evaluated.