How do you know if a bottle is corked?

How do you detect whether a bottle is corked? Easy peasy! All you have to do is smell the part of the cork stopper that was in contact with the wine removed from the bottle that you have just opened.

If the wine smells of cork, then the bottle is probably corked. You can also pour the wine into a glass and sniff it, or even taste it, because these methods also allow you to detect the presence of cork. 

Why is a bottle corked?

The cork of cork stoppers comes from tree bark. If the tree in question has a disease, this will also affect the cork stopper, and the bottle in which it is found.