A corked wine does not mean a wine with small pieces of cork floating around in the glass. It is a word for a wine that has become contaminated with cork taint, which is caused by the presence of a chemical compound called TCA.
In the worst instances, the wine tastes of nothing but mold – which should be obvious. But there are many other times when the wine might just taste a bit flat or dull. Often, you can’t tell if the problem is cork taint, bottle variation, or any of the other things that can go wrong with wine.
The good news is that cork taint is increasingly less common. Screw-caps are a big part of the solution, as is improving technology in cork production. It hasn’t been eradicated, however – and TCA remains a major risk factor, especially with older vintages. Before the 2000s, it was estimated that cork taint affected one in every 20 bottles.