When you stick your nose in a glass of wine, what do you smell? Most of the time, the aroma will be fruity, floral or spicy. The wine may even be earthy or smell of smoked meats (as in a Northern Rhone Syrah), or buttery and tropical. All pleasant scents. But what if you smell rotten eggs, wet newspaper or a barnyard? More than likely that wine is flawed. And that's a wine you don't want to keep in your glass. If you're at home, dump it down the drain; at a bar or restaurant, send it back (more on this later).

One of wine's dirty little secrets is that there are bottles on the market that contained flawed, faulty juice. Some times a wine gets spoiled somewhere along the way in the winery, and some times it happens after bottling, during shipping or storage at a retail or restaurant location or even in your home. You know how wine is supposed to be stored at about 55ºF, in a dark space with low humidity and no vibration? This doesn't always happen.

I recently completed a course at the Culinary Institute of America in Napa Valley called "Sensory Analysis of Wine." The thing that made me want to take such a technical sounding course (which it wasn't) was learning how to identify flaws and faults in wine. I know many of the good aromas, but I didn't know the bad, or off aromas. It's possible I've sipped a few faulty wines but didn't know it and just thought the wine was funky. You've probably done that too, or perhaps you had a glass of wine you didn't like but couldn't say why. Most likely it was flawed.

We went through six common wine odor defects. Once you know them, you'll be able to smell them right away.

Oxidized -- The wine will smell like a sherry, and may smell stale, nutty or even like burnt marshmallow or stewed fruit. The wine's color can offer a clue too. Usually an oxidized wine will be turning a shade of brown -- brick red for reds, and golden to tawny for whites. An oxidized wine can mean it was subjected to hot temperatures, was not stored properly or was exposed to air. If you order a wine by the glass and it smells a little stale, ask how long the bottle has been open; it's probably been a few days. Not good. Keep in mind a newly opened bottle can also be oxidized.

Volatile Acidity -- Does that glass of wine smell like vinegar or remind you of nail polish remover or Easter egg dye? Volatile Acidity (also called VA) is the culprit, and it is a bacterial spoilage.

Sulfur -- I had a strong reaction to this glass, and it wasn't a good one. Stinky and offensive, hydrogen sulfide has the unmistakable scent of rotten eggs. While sulfur is used in winemaking to prevent microbes and bacteria, overuse or improper use can cause it to form hydrogen sulfide or dimethyl sulfide. (Not to be confused with sulfites.)

Brettanomyces -- For years I've heard the term "brett," and that some people love what it does to wine and others do not. But I didn't know what the heck it smelled like until this class. Think of cherry cough syrup, Band-aids, or smokey, barnyardy or horsey aromas. I'm told a sweaty horse blanket is a ringer for brett. Brettanomyces is a yeast spoilage. Old world wines may have a tiny amount of brett that some wine drinkers covet. You can also find brett in some Belgian Trappist beers

Cork Taint -- I know what a corked wine is. But I am still surprised at how many of my friends and family don't know it when it's stinking up their glass. This means that the wine's been spoiled, or tainted by a chemical called 2,4,6-trichloroanisole, or more commonly TCA, that can develop in cork. When I smell corked wine, it's wet newspaper, dank basement, wet shaggy dog and musty. While the wine won't hurt you if you drink it, it's not a pleasant beverage because the cork taint will mask fruitiness. Open another bottle of wine -- odds are that even if it's from the same producer it's not corked. But get a new, clean wine glass. The corked odor hangs around even after you've dumped the wine out.

Sulfites -- Get a matchbook and strike a match. What you are smelling is sulfite. Sulfur dioxide is a sulfite, and a common antioxidant added to wine, to prevent bacterial contamination. You may get this odor from a newly bottled wine.

If you find any of these flaws in your wine glass, dump it out, send it back. Sure, sending a bottle back, especially an expensive one, is intimidating. The best way to handle this is to ask your server or the wine director to confirm what you are smelling. He or she should promptly send out a new glass or bottle. What gets people in trouble is sending back a wine because they don't like it. But wine and restaurant professionals realize that wine comes with faults. If you bought the wine from a grocery store or wine shop, cork it up and take it back to the retailer as soon as you can. You should get a replacement bottle or a refund.