The Effects of Micro-oxygenation on the Evolution of Red Wine Composition and Sensory Properties

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dc.contributor.advisor Kilmartin, P en
dc.contributor.advisor Nicolau, L en Nguyen, Dang en 2011-06-15T21:20:31Z en 2011 en
dc.identifier.uri en
dc.description.abstract Micro-oxygenation (MOX) is a technique that continuously delivers a small metered amount of oxygen into a wine by means of micro-bubbling using a porous micro-diffuser. MOX is considered an effective oxygen management tool for winemakers to produce particular wines in a consistent style. While several beneficial effects of MOX on wine quality have been well examined in scientific research, information regarding the influence of MOX on the reductive sulfur containing off-odours, sulfur containing substances mainly produce unpleasant smells which impart organoleptic defects in wine, the well-known as rubbery or 'reduced' character, is very limited. Of note is that the term 'reductive' here refers to sulfur containing volatiles with detrimental effects on wine quality, to distinguish them with compounds responsible for characteristic varietal aromas. An analytical method, using headspace-microextraction coupled with Gas Chromatography-Mass Spectrometry, was successfully developed and validated for the separation and quantification of up to fourteen reductive 'light' and 'heavy' sulfur containing volatiles. The effects of MOX were examined using different oxygen dosage rates before and after malolactic fermentation (MLF) on a Cabernet Sauvignon and a BORDEAUX blend, respectively, in replicated trials using 300 L stainless steel tanks and high density polyethylene tanks (Flextanks). A commercial scale MOX trial on an Australian Shiraz after MLF was also monitored. The analysis focused upon the evolution of the chemical composition, especially the reductive sulfur compounds. Effects on the wine post MLF at the end of the MOX treatments in terms of the perceived sensory characteristics have also been investigated. Limited oxygen exposure stimulated wine colour development, with positive effects still observed when spontaneous MLF occurred during the MOX operation. A significant influence of oxygen on tannins was only seen in the Australian Shiraz with prolonged oxygenation. MOX had fairly limited effects on individual polyphenols, except for the highly oxidisable flavan-3-ol epicatechin and the monomeric anthocyanins. Oxygenation did not affect the desirable varietal thiol 3-mercaptohexanol (3-MH), but resulted in a lowering in the concentrations of most reductive sulfur compounds. These observations were reflected in the sensory characteristics of the finished wines. The research provides insights into the effects of MOX on the reductive sulfur compounds in terms of both quantitative and sensory perspectives, alongside the effect upon other wine constituents including the polyphenols. The results indicated that the chemical mechanism leading to a decrease in the off-odour methanethiol is more likely to be linked with oxidised wine polyphenols rather than from a direct oxidation to a disulfide. Increase in the content of dimethyl sulfide may come about from chemical transformations occuring during wine storage. en
dc.publisher ResearchSpace@Auckland en
dc.relation.ispartof PhD Thesis - University of Auckland en
dc.relation.isreferencedby UoA99215798514002091 en
dc.rights Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. Previously published items are made available in accordance with the copyright policy of the publisher. en
dc.rights.uri en
dc.rights.uri en
dc.title The Effects of Micro-oxygenation on the Evolution of Red Wine Composition and Sensory Properties en
dc.type Thesis en Chemistry en The University of Auckland en Doctoral en PhD en
dc.rights.holder Copyright: The author en
pubs.peer-review false en
pubs.elements-id 211856 en
pubs.record-created-at-source-date 2011-06-16 en

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