Why Good Wines Go Bad
A Fresh Look at Closures, Wine Transport, and Storage.
It's a rare occurrence to purchase a bottle of wine from a reputable source only to find upon opening it that it's gone bad. We know that cork-finished wines have had a contamination rate around 5%, but this article is not about cork taint. It's about spoilage and what causes it.
There are two major types of spoilage: oxidation and reduction. We'll explain these terms in the following paragraphs.
Oxidation Spoilage
Oxygen is a necessary component of most life forms, animal and vegetable. But it is also a killer. When oxygen combines with organic or inorganic chemicals, a process called oxidation takes place. Iron turns to rust in the presence of oxygen. Human bodies display the products of age. And wine spoils. Oxidized wine reduces the complex flavor profile of wine and eventually turns it to vinegar. This happens when a wine is left open too long. Both red and white wines take on a brownish cast known as Maderization.
But oxidation can occur inside the bottle before it is opened. The common wisdom is that minute amounts of oxygen pass through or around cork closures. The answer to this is supposedly the screwcap or technological closures like the ZORK.
Reduction Spoilage
Reduction is the opposite of oxidation. Wine in an absolutely sealed environment is denied the benefits of micro-oxygenation and sulfur compounds become dominant. In time, wines that have been subject to a reductive environment become stinky and undrinkable. Reduction should not be confused with the effects of brettanomyces, or "brett," which also can make a wine smell slightly sulfurous. Reduction takes time, often years. Brett infection is obvious upon opening the wine and taking a whiff.
What Winemakers Are Thinking
Not every winemaker agrees on the factors that lead to spoilage. A recent poll conducted by Curtis Phillips of Wine Business Monthly revealed that around 43% of polled winemakers believed that some oxygen ingress through the closure was desirable. 33% held the opposite opinion. So the jury's still out even after the immense enological progress of the past decades.
Pressure—Another Spoilage Factor?
A spoilage factor not often considered is the pressure of the inert gas that occupies the headspace of the bottled wine. Headspace is the space between the top surface of the wine and the bottom of the closure —typically around 3/4 inch. At the time of filling, the pressure of this gas is one atmosphere. If the temperature of the wine is raised by 5 degrees, the pressure becomes around three atmospheres or around 42psi. In typical transport to market, a bottle of wine might experience a temperature shift of 30, 40, or more degrees. If left inside a hot automobile trunk, perhaps even more. This puts tremendous pressure on the closure and is a source of cork failure. (And the main reason why sparkling wines are always fitted with a wire cage.) If you remove a capsule and find the cork slightly higher than the top of the bottle, temperature is undoubtedly the culprit. Don't open the wine; take it back.
An interesting twist on the pressure issue is the well-established practice of storing wine bottles on their sides. Traditional wisdom was that the wine kept the cork from drying out. But today some winemakers believe that the greatest benefit is to move the headspace away from the closure.
Conclusion
Practical tips: Don't leave wine (especially red wine) open for more than a day or two (or a little longer if refrigerated). Don't leave wine inside a hot automobile (or any other hot place). Don't open a wine with a visibly damaged closure. Don't store wine upright for longer than a few weeks. Don't confuse reduction with brett infection. Don't confuse oxidation with volatile acidity (a vinegary smell and taste). Oxidized wines will exhibit a color change.
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