Winemaking: A Cyclical Dance of Oxidation and Reduction
Winemaking, when viewed through a biochemical lens, reveals itself as an elegant cyclical dance between oxidation and reduction. These two opposing yet interconnected forces shape the grapevine’s lifecycle and profoundly influence the character of the resulting wine.
Winter: Oxidation and Dormancy
Winter marks the vineyard’s dormancy, a period akin to oxidative rest. Vines pause their metabolic processes, and oxidative conditions predominate. Pruning wounds, cold temperatures, and weathering expose plant tissues, facilitating natural oxidative processes that reset and prepare the vine for the coming season.
Spring: Reduction and Vigorous Growth
With spring, the vineyard awakens and enters a reductive phase. Bud break and shoot growth occur rapidly, driven by reductive biochemical pathways where energy is conserved and synthesized. Chlorophyll production surges, converting sunlight into chemical energy and fueling vine growth.
Flowering and Pollination: Brief Oxidation
The flowering period introduces a brief oxidative shift. Exposure of floral structures and pollen to oxygen triggers oxidative reactions necessary for successful pollination, ultimately affecting fruit set.
Fruit Set, Berry Growth, and Veraison: Reduction Reigns
Post-pollination, the vine returns to reduction. Fruit set initiates rapid berry growth, where complex biochemical synthesis takes precedence. Organic acids, sugars, phenolic compounds, and aroma precursors are produced under tightly controlled reductive environments within berries, setting the stage for future wine character.
Ripening and Field Oxidation: Preparing for Harvest
As ripening progresses, berries become more permeable, and subtle oxidative conditions set in. Berry skins soften, color changes occur, and sugars concentrate. These controlled oxidative reactions help soften tannins and adjust aroma compounds, leading to balanced maturity.
Harvest: Peak Oxidation
Harvesting represents an acute oxidative moment. Mechanical damage, exposure to oxygen, and enzymatic activities rapidly initiate oxidative processes. This phase is carefully managed to prevent undesirable oxidation, protecting flavor integrity.
Fermentation: A Reductive Transformation
During fermentation, grapes undergo a dramatic shift back to reduction. Yeast consumes oxygen quickly, producing ethanol, carbon dioxide, and numerous reductive byproducts. This anaerobic environment protects sensitive aromatic compounds and promotes the synthesis of desirable aroma precursors.
Barrel Aging: Gentle Oxidation
Wine aging in barrels once again gently introduces oxygen. Micro-oxidation through oak barrels softens tannins and adds complexity and maturity to the wine.
Bottling: Another Oxidative Step
Bottling exposes wine briefly but notably to oxygen, marking another oxidative moment. Advanced bottling machines help manage bottling carefully, minimizing oxygen ingress to preserve freshness and sulfur dioxide to steward the wine into its young life.
Bottle Aging: A Final Redox Dance
Bottle aging can swing either oxidatively or reductively, depending on the microbiology, reductive capacity of the wine, bottling practices, closures, and storage conditions. For example, a burst of oxygen from bottling may set off a biological response from the wine's residual flora. Yeasts like Saccharomyces, Zygosaccharomyces, and Hanseniaspora can metabolize residual nutrients resulting in aroma and biogenic amine formation coinciding with the reductive shift in bottle. It can be a beautiful thing, having a similar allure of odorous French cheeses that blow off over the course of an hour to reveal fruit, spice, flowers, and other subdued aromas.
The modern grape grower and winemaker has a plethora of tools and techniques to shift the balance of this conceptual framework. Understanding the rhythmic interplay of oxidation and reduction throughout the winemaking process empowers winemakers to craft wines with precision even amid a changing climate.
