The Powerful Impact of Oxidation in Your Wine

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Nick Antonaccio
Nick Antonaccio

Last week I reported on the state of the cork industry. Improvements in cork technology and techniques have met the competing challenges of alternative bottle closures such as the screwcap and synthetic material. The incidence of cork taint, the result of traditional cork processing, has declined significantly, rendering it a minor concern of consumers.

However, cork and alternative bottle closures contribute to an additional potential off-putting aromas and flavors to wine. This phenomenon, wine oxidation, was the subject of a seminar I attended several weeks ago.

Dr. Paulo Lopes, head of research at Amorim Group, the largest producer of natural corks in the world, presented an enlightening interactive session sponsored by the Portuguese Cork Association in conjunction with the Cork Quality Council and arranged by Colangelo & Partners, a leading wine and spirits communications agency. Lopes focused on the effect of closures on wine taint. He presented scientific data and the results of numerous cause-and-effect studies.

This week I present a summary of his remarks and findings. The following information was culled from my seminar notes and the materials presented.

Cork allows wine to breathe as it ages. Tiny amounts of oxygen that penetrate the bottle over time allow the wine to improve as it ages. However, wine, in its most elemental form, is a fermented fruit derivative and is perishable. It’s just a question of time before oxygen accomplishes its dastardly deed – oxidation and spoilage.

There are a number of sensory signs of wine oxidation:

1) Color. Whites turn a golden-brown; reds a brick red or even brown color. 2) Aroma. Whites have apple cider notes; reds smell of cooled fruits. 3) On the palate. Dry, bitter characteristics dominate an oxidized wine.

Oxidation can occur anywhere in the winemaking chain. In the vineyard, a lack of nitrogen in grapevines promotes oxidation. In the winery, poor techniques in crushing and fermenting grapes may cause “premature oxidation” a term attributed to a spate of oxidized wines produced in the famous Burgundy region of France in the last few years. Excess oxygen during these processes may doom a wine well before it is bottled.

On its path to the safety (minimal oxygen) of being pumped into bottles, the simple process of transferring wine juice through pumps, coupled with interim storage in porous wooden barrels may introduce potentially debilitating oxygen into the developing wine. Most winemakers add sulfites to wines in an effort to counter oxidation, thereby prolonging the life of a bottle of wine.

It would seem logical that once wine is bottled, the minor amount of air space in the neck renders the wine safe from oxidation until it is opened. This is not necessarily so.

The bottle closure plays a role in potential oxidation as well. The most effective closure? Screwcaps, followed by cork products. A very distant third is synthetic cork. To place this in relative terms, screwcaps produce 2 mgs. of oxygen per liter of wine over time, compared to 3.5 mgs. for cork and a whopping 9 mgs. for synthetics.

The reasons for the intrusion of oxygen in sealed bottles are numerous. It typically enters through the sidewall of a bottle. The design and construction of screwcaps create the narrowest channel for oxygen to permeate a bottle. On the other hand, cork closures may permit oxygen to enter a bottle through the fibers of its material composition. As a cork ages, it dries out, creating a wider channel for oxygen to permeate a bottle. Laying a bottle on its side at a slight forward angle maintains sufficient moisture to prevent the cork from drying out, although the contact of wine with the cork exposes it directly to oxygen, somewhat defeating the benefit over time. Synthetic closures are rigid and unchanging, permitting oxygen the widest channel to permeate a bottle.

Wines are living, breathing organisms, constantly interacting with their environment. As with humans, each is unique and may defy expectations as they age. Hope for the best, be prepared for the worst and savor the unexpected.

Nick Antonaccio is a 40-year Pleasantville resident. For over 20 years he has conducted wine tastings and lectures. Nick is a member of the Wine Media Guild of wine writers. He also offers personalized wine tastings and wine travel services. Nick’s credo: continuous experimenting results in instinctive behavior. You can reach him at or on Twitter @sharingwine.


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