Q: I opened a bottle of wine and it smelled sour, a bit like vinegar. Is it safe to drink?—Philip, Toronto
A: It sounds like your bottle is affected by a common wine flaw known as volatile acidity (or VA for short). VA is primarily caused by ethyl acetate and acetic acid (the same acid found in vinegar). These molecules are said to be volatile not because they have a short temper, but because they vaporize at low temperatures—that’s why they have such a powerful impact on how a wine smells. In small amounts, VA can be a desirable attribute of a wine’s aroma profile, where it may contribute subtle oxidative notes and make other aromas pop. Some styles of wine would be unrecognizable—and much less compelling—without a little bit of VA. But too much is considered a fault. A lot of VA can make a wine smell off-puttingly sour and even like vinegar (heady notes of varnish, Magic Marker or nail-polish remover are other common descriptors).
What Causes Volatile Acidity?
Dr. James Osborne, a microbiologist at Oregon State University, told Wine Spectator that volatile acidity happens thanks to two chemical processes: chemical oxidation and microbial oxidation. In the first, exposure to air causes alcohol to oxidize, either during winemaking or in the bottle. When this happens in an oxidative wine, the results are likely intentional, controlled and desirable. But if the wine is exposed to too much oxygen at the wrong time—due to a faulty cork or the failure to keep barrels topped up during aging—you may end up with high levels of VA.
The second process, microbial oxidation, occurs when acetic acid bacteria (called Acetobacter) convert ethanol in the wine to the compounds responsible for VA. These bacteria are usually controlled by filtering and the use of sulfur, but if they are present in the wine and have access to oxygen, things can get out of hand.
Can Volatile Acidity Make You Sick?
Too much VA can be unpleasant, but experts say it’s unlikely to cause any health problems. While high concentrations of acetic acid can irritate the eyes, skin and mucous membranes, the amounts found in wine are quite low. Even in a badly flawed bottle, the amount of acetic acid will be much lower than in vinegar, which itself is not harmful to consume. Dr. Gavin Sacks, a food science professor at Cornell University, told Wine Spectator that “one would need to consume an unrealistic amount of wine” to reach harmful levels of acetic acid. And Dr. David Jeffery, a professor of wine science at the University of Adelaide, points out that some people even drink small amounts of vinegar as a health tonic.
Dr. Sacks emphasized that unlike potentially harmful microorganisms found in other foods and beverages, the acetic acid bacteria found in wine “will not grow uncontrollably in the GI tract nor produce highly toxic compounds.” Before the advent of modern water treatment, wine’s microbial safety—which is enhanced by its low pH and high alcohol content—often made “dilute wine ... generally safer than the local water supply.”
It’s also interesting to note that the old adage about all wine eventually turning to vinegar isn’t quite true. While an open bottle of wine exposed to air will oxidize (and VA will increase as a result), not all of the ethanol will be converted to acetic acid. Making vinegar requires special conditions and the introduction of particular kinds of microbes, which generally aren’t the same strains of acetic acid bacteria found in wine. Even if a wine seems to have turned completely sour, its concentration of acetic acid is likely still much lower than that of actual vinegar.
What About Other Wine Flaws?
Don’t miss our past Health Q&As on other wine faults, including corkiness (or TCA), brettanomyces and lactic acid bacteria spoilage. While faults are fascinating—and unpleasant—they generally present little reason to worry about your health. Dr. Sacks points out that “the major compound of health concern in wine is (of course) ethanol, and for most wines (even faulty wines) this will still be the main toxicant.” Whatever your vinous pleasure, moderation remains a wise approach.
As always, consult your healthcare professional about incorporating wine into a healthy lifestyle.—Kenny Martin
