Influence of Fermentation Water on Stable Isotopic D/H Ratios of Alcohol Obtained from Concentrated Grape Must.

According to Organisation Internationale de la vigne et du vin (OIV) standards, when analysing the stable isotope ratio of deuterium to hydrogen D/H at the methyl (I) and methylene (II) site of ethanol from concentrated must, a dilution with tap water is needed in order to carry out the alcoholic fermentation. This dilution causes a partial transfer of water hydrogens to the sugar, and this affects the (D/H)I and (D/H)II isotopic values of ethanol, which need to be normalised through specific equations based on the analysis of water δ18O or δ2H. The aim of this study was to evaluate the effectiveness and correctness of these equations experimentally. Grape, cane, and beet sugar, as well as grape must were diluted with water with increasing H and O stable isotope ratios, fermented, and analysed. SNIF-NMR and IRMS techniques were applied following the respective OIV methods. The equations based on the δ2H analysis of the diluted sugar/must solutions proved to be reliable in all the cases, although it is not an OIV standard. When using the equations based on the values of δ18O of the diluted solution, data normalisation was reliable only in cases where the water used for dilution had not undergone isotopic fractionation due, for example, to evaporation. In these cases, δ2H should be analysed.

Balsamic type varietal vinegar from cv. Xinomavro (Northen Greece). Optimization and scale-up of the alcoholic fermentation step using indigenous multistarters.

Taguchi design was used to examine the effect of parameters that should be optimized in order to control the alcoholic fermentation of the concentrated grape must (CGM) from cv. Xinomavro using the best-performing indigenous Hanseniaspora uvarum and Saccharomyces cerevisiae strains as multistarters. The "optimum" combination of conditions (cell ratio of H. uvarum/S. cerevisiae; inoculum size and inoculation time of S. cerevisiae; fermentation time and temperature) resulted in an alcoholic product that meets ethanol (79 g/kg) and residual sugar (164 g/kg) content requirements for further use in the production of balsamic type vinegar. Multistarter fermentation affected positively the varietal organoleptic traits of the fermented CGM. 5-(Hydroxymethyl)-furfural content emerged as a critical factor for the standardization of this process. Scaling up experiments in 12 L barrels verified findings from small scale in 100 mL flasks. The results of this work can be used as a prototype in further similar efforts.

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.