Managing Oxygen During Winemaking
(book excerpts)Many factors influence the winemaking process. Among them, is oxygen which can influence every stage of the winemaking process from the crush pad to bottling. The role of oxygen during winemaking is extremely complex. This is due to the fact that oxygen is used by both yeasts and bacteria and is a substrate for numerous chemical transformations. Traditional winemaking is considered oxidative, meaning that the wines are exposed to air (in open-top fermentors, for example, or during racking). With the advent of refrigeration, stainless steel tanks and inert gas technology, winemakers developed ways to protect their wines, creating another style of winemaking known as reductive winemaking. While oxidative winemaking is conducted in the presence of oxygen, reductive winemaking is conducted in the relative absence of oxygen. The redox potential effectively refers to a wine's state of balance between the oxidative and reductive capacity of the environment. Oxygen can play an important role during the winemaking process as it takes part in enzymatic and nonenzymatic oxidation reactions. Microbial oxidation is the result of aerobic spoilage microorganisms such as acetic acid bacteria and yeasts - Candida and Brettanomyces. Insufficient oxygen can prevent the softening of mouthfeel characters and favors excessive accumulation of reductive aroma compounds, such as hydrogen sulfide and mercaptans, which can be highly detrimental to wine aroma quality. At the same time, excessive exposure to oxygen can cause oxidative spoilage of wine, with irreversible loss of fruity and floral varietal aromas. Therefore, from a practical point of view, the challenge lies in determining the optimal degree of oxygen exposure that will allow a given wine to best express its aroma and palate characteristics.
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Topics Within This Chapter:
- Types of Wine Oxidation
- Enzymatic Oxidation
- Conditions Affecting PPO Activity
- Non-Enzymatic Oxidation
- Microbial Oxidation
- Impact of Oxygen on Wine
- Oxidative versus Reductive Wine Production
- Oxidative Winemaking
- Oxidizing Agents
- Oxidative Winemaking Techniques
- Reductive Winemaking
- Reducing Agents
- Reductive Winemaking Techniques
- Redox Potential
- Hyper-, Macro-, and Micro- Oxygenation in Wine Production
- Hyper-Oxidation
- Practical Considerations
- Macro-Oxygenation
- Micro-Oxygenation
- Chemical and Sensory Effects of Micro-Oxygenation
- Recommended Parameters for Micro-Oxygenation
- Stages of Winemaking
- Monitoring the Progress of Micro-Oxygenation
- Micro-Oxygenation Systems
- Use of Oak Chips
- Inert Gase Use in the Winery
- Argon
- Nitrogen
- Carbon Dioxide
- Uses of Inert Gases
- Sparging
- Flushing
- Blanketing
