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A Technical Guide for Wine Producers
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Using micro-oxygenation to improve wine quality
Quality in wine is largely determined by balance. This applies to the various components as well as the extent to which various vinification techniques are used. Oxygen or air in a less pure form is generally considered detrimental. The correct use of micro-oxygenation may have a very positive impact on wine quality.
The deliberate, measurable application of oxygen to wines is a relatively new practice, which may yet see interesting developments. Phenol compounds play a decisive role in the colour and mouthfeel of wines and are largely influenced by oxygen reactions. Red wines that are kept in barrels usually have a more intense colour and softer tannins than those in steel tanks. The difference between the two storage methods is oxygen exposure, which applies in the case of the barrels, the latter being porous. Limited oxygen exposure causes a decrease in free anthocyanin content, which heightens the colour intensity, while increased phenol polymerisation results in a softer taste. The purpose of micro-oxygenation is consequently also to change the phenolic and flavour characteristics of wine by means of managed oxygen application. The oxygen saturation level of wine is 6.3 ml/litre wine at 20°C. An estimated 15 to 20 ml oxygen/litre wine/annum is added to the wine during barrel storage and if oxygen exposure during racking is added to this figure, as much as 30 ml oxygen/litre wine may be added to the wine in the course of a year’s barrel maturation. The ability of a wine to accommodate oxygen exposure positively is determined, inter alia, by its quantitative and qualitative phenol content. During normal racking of wine it is difficult to determine the amount of exposure to oxygen and the consequences this may have on the wine; micro-oxygenation, on the other hand, is a controlled process where the winemaker is able to determine the amount of oxygen. Although this could potentially be a handy vinification practice, its application demands discretion (Zoecklein, 2007).
Micro-oxygenation (MOX) was developed in France in 1991 by Patrick Ducournau, after he found that red wine made from the cultivar Tannat, which is rich in tannins, became softer, more balanced and richer with exposure to oxygen. In order to have more control over the oxygen exposure, he developed an apparatus with which it could be regulated. This has been used in the rest of Europe since 1995 and in the USA since 1998. Micro-oxygenation usually takes place in two phases. The initial structuring phase often gives the impression that the technique has negative consequences and the benefits only become apparent during the second harmonising phase. The tannins undergo different phases which may be described as green, hard, firm, round and soft. Depending on the wine in question, the influence differs; this in turn impacts on the decision whether and how to use it. Wines with high tannin and anthocyanin levels benefit most from MOX in which case application should take place as soon as possible after alcoholic fermentation and before malolactic fermentation. Wines to be treated should be fined thoroughly, as any murkiness or cloudiness will absorb some of the oxygen. If oxygen exposure is to imitate barrel storage, the dosage should be 1 to 2 ml oxygen/litre wine/month. It is also possible to reduce problems such as a vegetative character or sulphurous flavours by using MOX. In both instances the process should take place as soon as possible. The best strategy is to supplement possible yeast nutrition deficiency at the alcoholic fermentation stage and to remove the sulphuric compounds that have formed with a high application of oxygen. Several trials have confirmed that the style of wines in steel tanks approximates that of barrel matured wines if MOX is applied and MOX can also be used to good effect in the case of premium wine, provided the winemaker does so with the necessary discretion. Although wines may be market ready at an earlier stage if MOX takes place, this does not necessarily imply that such wines have less bottle maturation potential (Cutler, 2009).
Mobile MOX units may be used to apply the dosages to tanks, barrels and during fermentation, but the diffusing function for the different actions will differ. MOX equipment measures oxygen/volume in millilitres. The micro-oxygenation tempo is consequently calculated as ml oxygen/litre wine/month. The volume of gas will be influenced by the pressure, however. PARSEC equipment consequently measures the tempo in mg oxygen/litre wine/month, while OENODEV VISIO 6 has equipment that is able to measure it in both forms. If the decision is taken to purchase MOX equipment, cellars should first decide which products to treat and use this as a basis for determining the size of the base unit and the number and type of spargers to be used (Philips, 2009).
References
Cutler, Lance. 2009. Industry Roundtable: Micro-oxygenation. Wine Business Monthly, April 2009: 28 - 35.
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