There are very few bad wines in the world compared to 20 years. And if there are any real bad bottles of wines, it is actually the wine bottle itself, that is a bottle that was handled incorrectly so that the wine inside got ruined. One example would be a bit of the cork getting in the wine and causing a very acidic taste to it. Many will agree what causes a wine to go bad and there are many factors that come into play.
Moldy fruit used to make the wine will cause it to go bad. Wine grapes that have that dusty, cardboardy taste to it and then used to make wine will obviously make it taste terrible. That is something to stay away from.
Due to the technology or careful winemaking, many wines stay in the wine stage. Wine is basically just going through the process between grape juice and vinegar. If the wine has crossed the line toward vinegar, then you know it is a terrible wine.
When taking a whiff of wine, if you can smell something chemical or bacterial, then it is of low-quality. The most common smells are acetone (nail polish thinner) and sulfur flaws such as rotten eggs, burnt rubber and bad garlic.
Wine that has been oxidized will have a particular smell of flatness, weakness or even a bit cooked yet it may taste the same. Oxidation of wine occurs when air, basically oxygen, has somehow gotten into the wine and killed it. Bad bottles usually cause this to happen.
Unfortunately, an excellent bottle of wine can be stored or shipped in high temperatures, causing it to taste cooked or baked. Often the leakage from the cork indicates that the wine has been ruined by high heat.
The most common issue with wine has to due with corky wine. This is caused by a bad cork, when the smell of damp cardboard from the cork permeates the air and damages the once excellent wine. Once again, this is caused by a bad bottle.
It is important to note, that most wines are excellent tasting. Usually a bad bottle is due to the bottle itself. When choosing a bottle of wine, be aware of the way the wine was shipped, the shape the cork may be in. Those are some ways to prevent yourself from drinking a bad a bottle of wine. But once opened, you can normally observe it is bad by smelling it before you have the misfortune of drinking it.