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Schneider - Oenologie
Volker Schneider
Rupertusweg 16
55413 Weiler bei Bingen
Germany

E-Mail: Schneider.Oenologie@gmail.com

Scientific


Oxygen consumption by postfermentation wine yeast lees: Factors affecting its rate and extent under enological conditions.
In: Food Technol. Biotechnol. Vol. 54, No. 4, 2016, 395-402.
Postfermentation wine yeast lees display antioxidant properties based on their ability to consume dissolved oxygen. Their oxygen consumption rate depends on their amount, the yeast strain, and temperature. It is strongly decreased by free SO2, thus excluding additional effects of both as antioxidants in wine. It cannot totally prevent concomitant chemical oxidation of the wine but interferes seriously with micro-oxygenation of red wines.
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Chemical and sensory discrimination of different kinds of white wine aging and enological measures to improve white wine flavor stability:  A Review.     
In: Recent Advances in Wine Stabilization and Conservation. A.M. Jordao and F. Cosme (Ed.), Nova Science Publishers Inc., 2016.
An extensive review on white wine aging and technical means to improve white wine flavor stability, with references updated until 2015. 
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Evaluation of small amounts of flavonoid phenols in white wines by colorimetric assays
In: Am. J. Enol. Vitic., Vol. 46, No. 2, 1995, 274-277.
Flavonoid phenols are responsible for astringency and accelerated oxidative aging in white wines; they do not correlate with total phenols. For their measurement in the low concentration range in white wines, four colorimetric assays have been compared. The reaction with 4-(dimethylamino)-cinnamaldehyde displays highest specifity, sensitivity. and reproducibility. It appears most suitable for the appreciation of oxidative aging potential in routine control.
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Must hyperoxidation: A review
In: Am. J. Enol. Vitic., Vol. 49, No. 1, 1998, 65-73.
When white grape must is processed without sulfur dioxide, enzymatically induced oxidation occurs and leads to a precipitation of phenolic compounds as insoluble brown pigments. Wines obtained from oxidized juices are reported to display more resistance against oxidative quality degradation during aging. Hyperoxidation makes use of a deliberate oxidation prior to fermentation in order to improve wines's shelf-life. Sensory results are derived basically from the flavonoid removal involved. This review deals with the reactions involved, analytical control, chemical and sensory consequences, and the reasons for conflicting sensory results of hyperoxidation.
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Atypical Aging Defect: Sensory Discrimination, Viticultural Causes, and Enological Consequences. A Review.
In: Am. J. Enol. Vitic., Vol. 63, No. 3, 2014, 277-284.
Untypical aging is an off-flavor which can occur in white wines within a period of a few weeks to one year after the first addition of sulfur dioxide post fermentation. Its sensory characterization is varied and controversial. Most research agrees on 2-aminoacetophenone and other less well identified compounds generated by degradation of indole-3-acetic acid as the causal agents. This chemical pathway is controlled by the oxygen radical scavenging capacity of the wine which, in turn, is highly influenced by viticultural stress factors as the ultimate cause. Although oxygen is involved, untypical aging is distinct from premature oxidative aging with its own set of sensory and chemical descriptors.
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Vines take up yeasts from soil and transport them through the vine to the stem and skins of grapes.
In: Ithaka-Journal 2015, Arbaz, Switzerland, ISSN 1663-0521, pp. 349-355, www.ithaka-journal.net/85
In a vineyard field experiment, it was demonstrated that S. cerevisiae yeast can be adsorbed from the soil by the roots of V. vinifera sub. vinefera and transported via vine to the stems and surfaces of the grapes. To exclude any extrinsic yeast contamination, the ripening grapes were sterilized and wrapped in plastic bags. Eleven yeast strains were then spread onto the vineyard soil. At four time points, grape samples were taken under sterile conditions, crushed, and fermented without further inoculation. Using PCR fingerprinting and microsatellite PCR, it was demonstrated that the yeasts in the fermented must were from the same yeasts spread on the vineyard soil.
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