The waiter arrives with the bottle and expertly turns it so you may peruse the label. Hmmm, you say, "yes, that's the wine I ordered all right." And then, that moment of truth arrives.
He uncorks the bottle and delicately holds the cork under your nose, or worse yet, he hands the cork to you, placing it gingerly upon the palm of your hand. What do you do? Sniff lightly and nod, returning the cork as quickly as possible? That's one reaction.It's true that sniffing a cork can tell you something. One thing it can NOT do is tell you if the wine is bad. Mostly what you'll discover when you sniff the cork is how the cork smells. To determine if your wine is good, you'll have to smell and taste the wine yourself.
So why do some sommeliers present the cork to you at restaurants? Today, it's mostly tradition. Sometimes, it's because they saw someone else do it in a fancy restaurant and thought it looked good. It became common practice to present the cork when inexpensive wines were sometimes fraudulently transferred into bottles with prestigious labels. This dates back to a period more than a century ago, and is not a common occurence today. The idea was for the customer to see that the brand printed on the cork matched the brand and vintage printed on the label.
Most corks are still labeled, so you can match the cork to the wine label. Another thing you can look for when you are holding the cork is firm and wet end. If the end of the cork is dry and/or crumbly, you can expect the wine to be less than stellar. There's a good possibility that air was introduced into the wine before it was opened.
If the cork is firm, moist and springy to the touch, you can bet it did it's job.
So go ahead, uncork that wine and enjoy it!