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Neustadt an der Weinstraße, Germany

Durner D.,Kompetenzzentrum Weinforschung | Ganss S.,Kompetenzzentrum Weinforschung | Ganss S.,Institute For Lebensmittelchemie Und Arzneimittelprufung | Fischer U.,Kompetenzzentrum Weinforschung
American Journal of Enology and Viticulture | Year: 2010

Dissolved and headspace oxygen concentrations were monitored during microoxygenation (MOX) treatments before and after malolactic fermentation (MLF) of Pinot noir. The implementation of a noninvasive, fluorescence-based measurement system allowed precise oxygen determination in red wine and in the gaseous headspace above the wine surface. Dissolved oxygen (DO) concentrations increased up to 1 and 0.5 mg/L in the second half of pre-MLF and post-MLF MOX experiments, respectively. Untreated control wines showed maximum DO concentrations of only 0.1 mg/L at the end of the pre-MLF and post-MLF MOX trials. For both pre- and post-MLF MOX experiments, the measurement of DO was sufficiently sensitive to discriminate between untreated control and oxygenated wines. Furthermore, different levels of applied oxygen dosages could be differentiated using DO monitoring. Except for the end of post-MLF MOX treatments with high oxygen dosage, no DO gradients were observed within the tanks, suggesting appropriate oxygen distribution during the treatment periods. The novel concept to compare the rate of applied oxygen with DO lead to the expression of the oxygen consumption rate. Plotting this parameter together with the applied oxygen dosage allowed for the assessment of the balance between the ingress and the consumption of oxygen. During pre-MLF and post-MLF MOX treatments, the oxygen consumption rate was consistently ±10% of the applied oxygen dosage. However, wines receiving oxygen post-MLF reacted more sensitively to an elevated oxygen dosage than those treated pre-MLF. © 2010 by the American Society for Enology and Viticulture. All rights reserved.

Weber F.,TU Braunschweig | Greve K.,TU Braunschweig | Durner D.,Kompetenzzentrum Weinforschung | Durner D.,Kaiserslautern University of Applied Sciences | And 2 more authors.
American Journal of Enology and Viticulture | Year: 2013

The polyphenols of a 2005 Cabernet Sauvignon were fractionated by gel permeation chromatography. The obtained fractions were reconstituted in a model wine medium for analysis. The chemical properties of the fractions were investigated by HPLC-DAD, HPLC-ESI-MSn, colorimetric analysis, and additional chemical assays. Application of these different techniques and combination with the elution pattern of the gel permeation material revealed some valuable structural information. The early eluting fractions, which were larger in molecular size and/ or more polar than late eluting fractions, contained higher proportions of pigmented polymers and higher amounts of bound anthocyanins. These anthocyanins were responsible for the color properties of the early eluting fractions, which could be separated according to CIELab analysis. The later eluting fractions exhibited lighter, more yellowish color, provoked by the higher tannin concentration, and contained low molecular weight proanthocyanidins. Descriptive sensory analysis was carried out, assessing bitterness, sourness, and attributes describing different subqualities of astringency. Dry tannin intensity was rated lower for the early eluting anthocyanin-rich polymers compared to the later eluting fractions, which were rich in procyanidins and/or oligomerized flavan-3-ols. Accordingly, the attenuation of the astringent perception, as it is generally observed during red wine aging, may be attributed to increasing anthocyanin incorporation into the polymers. In contrast to astringency, the intensity of bitterness was not sufficiently correlated with any chemical parameter. This observation suggests that very specific phenolic structures are responsible for the bitter perception in red wines. As the high molecular pigmented polymers evoked lowest astringency ratings, the results of this study indicate that the increase of astringency due to higher degrees of polymerization can be substantially prevailed by the incorporation of anthocyanins into polymeric structures. © 2013 by the American Society for Enology and Viticulture. All rights reserved.

Slabizki P.,Kompetenzzentrum Weinforschung | Slabizki P.,University of Duisburg - Essen | Fischer C.,Rudolf Ohlinger GmbH and Co. KG | Legrum C.,Kompetenzzentrum Weinforschung | And 3 more authors.
Journal of Agricultural and Food Chemistry | Year: 2015

Natural cork stoppers with sensory deviations other than the typical cork taint were subgrouped according to their sensory descriptions and compared with unaffected control cork stoppers. The assessment of purge and trap extracts obtained from corresponding cork soaks was performed by heart-cut multidimensional gas chromatography-olfactometry (MDGC-O). The identification of compounds responsible for atypical cork taint detected in MDGC-O was further supported with additional multidimensional GC analysis in combination with mass spectrometric detection. Geosmin and 2-methylisoborneol were mainly found in cork stoppers described as moldy and cellarlike; 3-isopropyl-2-methoxypyrazine and 3-isobutyl-2-methoxypyrazine were found in cork stoppers described with green attributes. Across all cork subgroups, the impact compound for typical cork taint, 2,4,6-trichloroanisole (TCA), was present and is therefore a good marker for cork taint in general. Another potent aroma compound, 3,5-dimethyl-2-methoxypyrazine (MDMP), was also detected in each subgroup, obviously playing an important role with regard to the atypical cork taint. Sensory deviations possibly affecting the wine could be generated by MDMP and its presence should thus be monitored in routine quality control. © 2015 American Chemical Society.

Durner D.,Kompetenzzentrum Weinforschung | Weber F.,TU Braunschweig | Neddermeyer J.,Kompetenzzentrum Weinforschung | Koopmann K.,Kompetenzzentrum Weinforschung | And 2 more authors.
American Journal of Enology and Viticulture | Year: 2010

Different microoxygenation procedures before and after malolactic fermentation were applied to Pinot noir wines from two consecutive vintages using the same Pinot noir block and a standardized winemaking protocol. The effects of microoxygenation treatments were investigated by spectrophotometry, HPLC-DAD, and descriptive sensory analysis. Microoxygenation before malolactic fermentation was carried out in 250-L red wine fermentors at oxygen dosages of 20 and 100 mg/L/month for 20 days. Oxygen dosages of 1 and 5 mg/L/month were applied for three months after malolactic fermentation using 100-L stainless-steel tanks. CIELab results showed that microoxygenation in 2006 tended to yield light-colored wines with an increase in yellow tonality. Examining monomeric polyphenols after alcoholic fermentation, this oxygen-induced color loss may be related to the high flavan-3-ol to anthocyanin ratio in this vintage. Furthermore, twice the increase in acetaldehyde content upon microoxygenation after malolactic fermentation was observed in 2006, which indicated excess oxygen for these wines. By contrast, a low flavan-3-ol to anthocyanin ratio was determined after alcoholic fermentation in wines of vintage 2007. Predominantly, these wines showed an increase in blueness upon microoxygenation treatments. Low correlations among astringency related attributes proved that the chosen attributes independently characterized the sensory variation in tannic structure among the microoxygenated Pinot noir wines. Descriptive analysis revealed that microoxygenation predominantly diminished green tannins in 2006 wines. Dry tannins, although decreasing in course of microoxygenation with low oxygen doses, rose again at higher oxygen doses. Beneficial aroma changes in 2006 and the increase of color intensity in 2007 were more salient upon microoxy-genation prior to malolactic fermentation. An unfavorable impact on Pinot noir aroma occurred primarily due to microoxygenation after malolactic fermentation. © 2010 by the American Society for Enology and Viticulture. All rights reserved.

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