title_body: How do you know if wine has gone bad?
upvoted_answer: Here is a list from the Wine Faults Wikipedia page. These faults, for the most part, will not do any harm when they are in wine (they aren't strong enough) They just taste bad.
  
  Acetaldehyde    Smell of roasted nuts or dried out straw. Commonly associated with Sherries where these aromas are considered acceptable
  
  Amyl-acetate    Smell of "fake" candy banana flavoring
  
  Brettanomyces   Smell of barnyards, fecal and gamey horse aromas Cork taint Smell of a damp basement, wet cardboard or newspapers and mushrooms
  
  Butyric acid    Smell of rancid butter 
  
  Ethyl acetate Smell of vinegar, paint thinner and nail polish remover
  
  Hydrogen sulfide    Smell of rotten eggs or garlic that has gone bad
  
  Iodine  Smell of moldy grapes 
  
  Lactic acid bacteria    Smell of sauerkraut 
  
  Mercaptans  Smell of burnt garlic or onion 
  
  Oxidation   Smell of cooked fruit and walnuts. Also detectable visually by premature
      browning or yellowing of the wine 
  
  Sorbic acid plus lactic acid bacteria   Smell of crushed geranium leaves 
  
  Sulfur dioxide  Smell of burnt matches. Can also come across as a pricking sensation in the nose.