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  • Author or Editor: A. Leskó x
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During the course of research, the extractability of various phenolic compounds were analysed in ‘Blaufraenkisch’ berry skins and wines produced by six types of vine load. A sample of the berry skin was detached from the harvested crop and following the extraction with hydrochloric acid-methanol the composition of the extractive and the wines prepared by microvinification was analysed. During the course of the tests, the total polyphenolic-, anthocyanin-, leucoanthocyanin- and catechin content of the samples were measured by the application of the spectrophotometric method. Based on the measured data, the extraction coefficients (EC %) were calculated for each vine load, and then through the application of statistical methods, the data of three vintages were evaluated. The results revealed that extractability does not necessarily depend on the method of cultivation or the vine load. No significant differences were found pertaining to either the extractability of the total polyphenolic-, leucoanthocyanin- or catechin content. However, the extraction coefficient of the anthocyanins in crops produced by cluster selection and cane-based cultivation was significantly lower than in the cluster-selected crops of vine-stocks with less bud load.

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The sensory quality of red wines is basically determined by the colour, which depends on the amount and on the evolution of anthocyanins and other phenolic compounds extracting from the berries into the wine during wine-making. The anthocyanin-monomers are responsible for the development of the red colour, and their acylated derivatives provide stability for the colour of the wines. The anthocyanin profile of wines is affected by several factors: the grape variety, the conditions during wine-making, and also the yeast culture used for the fermentation. In our experiments a self-compiled model solution was fermented by spontaneous fermentation, as well as by four commercial yeasts under laboratory conditions. After fermentation total polyphenolics, anthocyanins, anthocyanin monomer profile, colour intensity, hue, and the ratio of polymeric anthocyanins were studied. Our results show that the spontaneous yeast fermentation resulted in a higher anthocyanin concentration in the fermented model solution, but the commercial yeast strains provided a more advantageous colour characteristic compared to the spontaneous fermentation. After the spontaneous fermentation less sediment was left than in the commercial yeast fermented samples.

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While keeping wines on the fine lees the composition of nitrogen-containing substances, including the amino acid concentration, changes as a result of the autolysis of yeasts. During the course of former experiments, it was proven that yeasts were able to reduce the polyphenolic composition of wines. As part of the research for the present publication, the change of polyphenolic content in ‘Chardonnay’ wines kept on the lees was analysed. In addition the quantity of tyrosol, required for the forming of simple phenolics, was examined. The results proved that yeasts reduced the quantity of polyphenolics. In addition, due to the increased amino acid concentration, yeasts reduced the quantity of tyrosol that is derived from the amino acid called tyrosine.

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