Managing Oxygen During Winemaking
Oxidative versus Reductive Wine Production
Oxidative and reductive winemaking are terms used to describe two contrasting styles of vinification. The processes are ideologically and scientifically opposed, and each has a profound impact on the aromas, flavors, and texture of wine. Both terms refer to the relative presence or absence of oxygen during winemaking. Oxidative winemaking aims for a higher, but controlled, presence of oxygen, while reductive winemaking aims to complete vinification with as little influence of oxygen as possible.
Oxidative winemaking aims for a higher, but controlled, presence of oxygen (i.e., the winemaker intentionally allows oxygen to interact with the wine during the winemaking process). Winemakers do so by introducing a controlled amount of oxygen at various stages of vinification. The aim of oxidative winemaking is to develop secondary aromas and flavors in wine and add textural complexity.
The most important oxidizing agent in musts and wines is oxygen. Heavy metals such as iron and copper that are normally present in wine can as powerful catalysts. They can strongly increase the action of oxygen and the rate of oxidation reactions.
Oxidative Winemaking Techniques
Options to create oxidized environments include: cold soak (lower temperature can increase oxygen solubility); hyperoxidation (Section 17.3); soft pressing; no skin contact and removal of stems; open top fermentors; cap management - pump-overs, punch-downs, and rack-and-return; cement tanks; macro-oxygenation (Section 17.3); tank to tank transfers; batonnage (stirring lees) (Section 8.5); racking, aging in barrels and topping operations; micro-oxygenation (Section 17.3); and bottle closure selection (Section 12.2).
In contrast, reductive winemaking means winemaking in more of an anaerobic environment without oxygen. Reductive winemaking is all about protecting the grapes, the must (juice), and wine so that the primary fruit aromas and flavors are preserved. The wines produced by reductive processes are usually fresh and vibrant, with varietal grape character as the primary aroma and flavor. White wines especially benefit from being treated reductively, showing fresher and cleaner aromatics.
The most important reducing agents (i.e., antioxidants) found in wine are phenolic compounds, sulfur dioxide, ascorbic acid, and glutathione. Phenolic compounds, which are responsible of the wine quality, are the principal substrates of wine oxidation. The phenolic concentration is an indicator for oxidation in wine, namely, higher phenolcontent oxygen.
Reductive Winemaking Techniques
Reductive winemaking is performed (as much as possible) without the presence of oxygen. The wine is protected throughout the harvest, fermentation, maturation, and bottling process from oxygen. Inert gases can be used to prevent product contact with air, using nitrogen, carbon dioxide, or argon. Minimizing transfers, racking, managing headspace, and other cellar operations will reduce the risk of air contact.
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