There has likely been a time or two when you've opened a bottle of wine and it has smelled and tasted a little off, perhaps a lot off. In these cases it is not your taste buds rebelling against the wine in question; it is probably because the wine is "corked". Now, corked is not a term that is used to describe those bits of cork that sometimes make their way into our glasses. Corked is a wine term to describe a bottle that has been contaminated and is essentially undrinkable.
There are various reasons for this and it's often debatable. Some people are staunch believers that corking happens strictly from a bad cork while others believe in the thought that the tainting may occur from wooden barrels, storage conditions of the wine and even transportation of the corks and wine. It's important to note that a corked wine has nothing to do with the original quality of the wine. Cork taint can affect wines irrespective of price and quality level. There is one undisputed reason for cork taint and that is the contamination of a chemical called 2, 4, 6-Trichloroanisole or TCA for short.
Cellar Notes has a good explanation detailing TCA contamination:
A'Corked' wine is a wine that has been bottled with a cork that is contaminated with TCA (2, 4, 6-Trichloroanisole). TCA contamination usually comes from corks but can also come from barrels, other cooperage or even, apparently, from wood within the cellar including walls or beams. The term 'corked wine' is applied to all wines with TCA contamination because corks are the source of most of the problems. The wine industry estimates that as many as 3% to 7% of all wines have TCA contamination at levels that can be detected by consumers. Because most people are not trained to recognize the smell and taste of TCA, only a very small fraction of these bad bottles are ever returned to stores or sent back at a restaurant.
Even a very tiny amount of TCA in a wine can ruin it. Most people become aware of TCA in quantities as small as 5 parts per trillion and some individuals are even more sensitive. When TCA is present in quantities high enough to be evident to a person, it comes across as 'musty' aromas and flavours. Even when TCA is not evident in the smell or taste of a wine, very small quantities can subdue the aromas and flavours of fruit that the wine would ordinarily exhibit.
TCA does not pose a health risk (at least in the levels found in wines). It just imparts the aromas and flavours that are objectionable when found in sufficient quantity. Many wines have levels of TCA that are below the threshold of perception. Wine is not the only place you can find TCA. It is also found in some municipal water supplies as well as in some teas.
A great deal of work continues in the cork industry as well as at wineries to develop methods to eliminate corked wine. So far, no completely reliable method has been found.
There are other causes of bad bottles of wine, but TCA contamination is the primary fault you will find in otherwise well-stored bottles. Other faults can include wines that are oxidized, lightstruck or have undergone unplanned secondary fermentation.
Detecting corked wine can sometimes be fairly easy with just a sniff of the wine. It will have a characteristic odour described as resembling a mouldy newspaper, mushrooms, wet dog, damp cloth, or damp basement. However there are times when it's a little more challenging to detect and the only way to do so is by tasting the wine. If this is the case, it will taste like all of the similar qualities above as well as tasting astringent and with a raspy finish.
Sadly there is no easy way to avoid a corked bottle of wine. Cork is a natural product and can be fair game for microorganisms. And if nature has taught us anything it's that not everything can be perfect all of the time.
(References: New York Magazine, Cellar Notes, the Wine Doctor. Photo Credit: RSC.org)