Bottle Briefing: Identifying the Faults That Make Good Wines Go Bad

Hand someone a carton of sour milk and they’ll push it away with an “Ew, no thank you!” But when good wine goes bad it’s not always so simple and straightforward.

Many consumers just aren’t familiar enough with wine flaws to confidently diagnose what’s wrong. And it can be scary to speak up since, despite the best efforts of many in the business, the world of wine is still a rather intimidating place.

Knowledge is power, though, so below are six common wine faults and tips on how to identify them.

What it is: Brett is short for Brettanomyces, a type of yeast that frequents wineries—it likes the phenols that make up red wine—imparting an earthy aroma to the wines it comes in contact with. This is one of the trickier flaws since some people enjoy a touch of Brett, and there are wineries that work with the quality rather than fight it.

How to spot it: Most commonly heralded by a smell of barnyard or Band-Aids. Dr. Linda
Bisson and her colleagues at the University of California, Davis, have tested dozens of strains of Brett and discovered that about a quarter of them add good flavors, including meaty, floral, and fruity notes. At the other end of the scale, though, it can add notes of rotten meat, sewer gas, and burnt beans. A hint of leather or bacon might not be a bad thing. A full-on hit of dog park probably means it’s time to send the bottle back.

What it is: This flaw is just as it sounds: The wine has been allowed to overheat. In the process it’s either lost some of its “oomph” or become flat-out stewed tasting, like over-brewed tea. This can be caused by a number of factors, like sitting on a loading dock in 80-degree temperatures, or being stored in a basement right next to the water heater. Most wineries try to avoid cooking their wines by not shipping in the summer or by using package inserts that register when temperatures go above tolerance levels. But overall, the average consumer is still pretty much at the mercy of suppliers.

How to spot it: Sometimes it’s easy. The cork might stick out from the neck of the bottle slightly, having been forced out as contents heated and expanded. Other signs include streaky wine stains on the sides of the cork. If the damage is not severe—cooked all the way—you might simply detect raisin-y, stewed fruit aromas in the wine.

What it is: A big problem and one that’s also easily misunderstood. After all, aren’t most wines corked—as in sealed with a cork? When used to describe a flaw, however, “corked” means that the wine has come into contact with a chemical known as TCA (short for 2,4,6-trichloranisole). This chemical typically forms when natural fungi come into contact with chlorophenols in plant matter. Exposure to TCA is harmless at low levels, but it will wreak havoc on wine. Although it can contaminate barrels and bottling lines, it is most closely associated with use of natural cork. Estimates vary on the amount of contamination exists today in the global supply of cork
stoppers. The commonly quoted figure is 3 percent, although other estimates are higher.

How to spot it: Despite what you may have seen in old movies, you’re not going to detect cork taint from sniffing the cork. It also has nothing to do with little pieces of cork that crumble into the wine. You’ll detect it by sniffing the wine and noticing a smell like wet, musty newspapers, wet cardboard, or moldy basement. It doesn’t take a lot of TCA to make an impact; most people can smell it at 10 parts per trillion. (For reference, one part per trillion is like mixing one drop of red dye into 20 Olympic-sized swimming pools.) Different people do have different sensitivities to TCA, though, so what reeks to one person might smell just slightly suspect to another. What really scares winemakers is that in lower concentrations you don’t find the telltale note of damp basement but are left with a wine that simply tastes a little off or muted. Those customers wouldn’t bring back the bottle—but they probably won’t buy another, either.

What it is: This is another of those good news, bad news issues. Oxidation is the type of spoilage that happens when you cut up fruit and leave it out on your kitchen counter. Some wines are improved by oxidation, and in fact their style is meant to be oxidized—think Madeira and Sherry. Also, older wines are pleasantly transformed by the tiny bit of oxygen that has passed through the cork during long storage and bottle age. But a fresh, crisp wine like a young Sauvignon Blanc will definitely suffer if it has gotten too much air.

How to spot it: This is where the eyes have it; color is a common tip-off to oxidization. Vivid reds turn brick-red or brown; whites darken to amber or gold-brown. In terms of aroma, white wines can smell like apple cider or Sherry. Red wines will smell flat and sometimes have a caramel quality.

What it is: This is the flip side of oxidation; the wine hasn’t gotten enough exposure to oxygen during its production and cellar and bottle aging, usually due to winemaking techniques aimed at reducing oxidation flaws.

How to spot it: A reduced wine gives off an odor of sulfur, like burnt rubber or rotten eggs. It can sometimes be fixed by decanting, and thus aerating, the wine. Another trick to ameliorate a reduced wine is to drop a small piece of copper, even a (clean!) pre-1980s penny, into the wine. The copper latches onto the sulfur molecules and makes them unavailable to your nose and tongue.

What it is: Volatile acid, known as VA, occurs naturally in wine and is usually caused when bacteria create acetic acid, the substance that gives vinegar its characteristic flavor. In small quantities it’s not a problem. But if particularly virulent bacteria take hold and the VA gets out of control—watch out.

How to spot it: You stick your nose in the glass expecting to smell wine. You get a sharp whiff
of vinegar or acetone. Often the wine will also taste like vinegar.

Here’s one more very common weird thing that can happen to wine: Sometimes crystals will accumulate in the bottom of a bottle that has rested in the refrigerator for a day or two. These crystals form when potassium and tartaric acid naturally occurring in the wine combine and sink out of solution. A good winemaker will stabilize the wine so it’ll withstand typical refrigeration temperatures without forming these crystals. But if it does happen, don’t worry. This flaw is harmless—and happily, it’s one that won’t affect wine’s taste.


  1. There is nothing common about any of these faults. Combined, they account for a few percent of total production. It’s certainly nice to be aware that they exist and how to detect them, but this evokes a false sense of importance and will detract from what should be an enjoyable experience by those who scare easily.

  2. You’re right. Incidence is generally low, but I do think it’s useful for consumers to know what to look out for so they don’t simply assume they don’t like that particular wine.

  3. From the somm side these are very common and this is a very important article for all in the wine business. It depends on your sources, but corked wine can account for around 3-7% of your total openings (I worked in a major casino where I believe TCA was in the central wine cellar, so the percentage there was around 15%). Being in Vegas, the occurrence of cooked wine can be around 3-5% and being in an Italian house VA and Brett are as common as people mispronouncing Bruschetta or dropping the last “e” in Amarone. I used this article to teach my staff about flaws. Thank you.

    As a side note I had a tasting room manager at a reasonably sized winery in St. Helena tell me that his wine he was tasting us on was not corked. My reply was simply “You mean the winemaker meant for the end product to taste like this?” It’s fine to say “I don’t get any TCA on this, but to flat out deny it? I grew up in the North East. I know what a moldy basement smells like.

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