Below are some of the faulty aromas sometimes found in wines. In some cases, these aromas are acceptable or even welcome in low concentrations, but are considered faults at higher concentrations.
- 2,4,6-Trichloroanisole (TCA) – A mold that can grow on and in the bark of a cork oak tree, on the winemaking implements, or even in the winery itself. Also known as corked or cork taint, although it is now known that infected corks are not the only source of this fault. Wines with this fault exhibit a musty, moldy odor similar to that of wet cardboard or a dark basement. In milder cases the wine may taste muted or seem less flavorful. TCA can be noticeable at relatively low concentrations. Once identified, the aroma is unmistakable.
- Odors resulting from sulfur compounds:
- Sulfur dioxide (SO₂) – Displays an acrid smell, similar to burnt matches. Directly related to pH, the more acidic the wine, the more pronounced the SO₂ will be.
- Hydrogen Sulfide (H₂S) – Displays the smell of rotten eggs. Caused by sulfur-rich wines that sit too long in the absence of oxygen, such as when a barrel or tank rests for an extended period with a large amount of yeast sediment in the bottom. This can also be a problem in wines closed with screw caps (which are impervious to oxygen).
- Mercaptan – Ethyl mercaptan may form as a combination of sulfur and ethanol, resulting in an unpleasant odor often described as smelling like garlic or onions. Mercaptan is the odor added to natural gas to help detect a leak. This defect is very serious and less remediable than the above defects.
- Odors resulting from action of bacteria – Although most bacteria cannot survive in the acidic environment of wine, the major exceptions are lactic bacteria and acetobacter. Such bacteria attack various compounds in the wine – changing the composition and sometimes producing carbon dioxide or other gases.
- Acetic acid – The odor of vinegar. “Volatile acidity” refers to a wine with the aroma of white vinegar.
- Butyric acid – The odor of rancid butter or spoiled cheese.
- Lactic acid – An odor described as being like sauerkraut or a goat.
- Ethyl acetate – The odor of fingernail polish remover or airplane glue. A common ester formed through a reaction of ethanol and acetic acid.
- Geranium fault – The odor resembling crushed geranium leaves, normally caused by the metabolism of sorbic acid via lactic acid bacteria.
- Odors resulting from other causes:
- Brett – Short for “Brettanomyces”, a member of the yeast family and can infect all parts of a winery or the wines produced there. Causes a “sweaty” or “horsy” odor or may simply deaden the primary flavors of a wine. Also described as “Band-Aid-like” or “medicinal”.
- Green – The odor of leaves, usually from the use of immature (underripe) grapes.
- Oxidized – Caused when oxygen reacts with some of the phenolic compounds. The resulting chemical oxidative reaction may create acetaldehyde.
- Maderized – A cooked or baked odor from excessive heating or oxidization.
- Moldy –The odor of mold from the use of moldy grapes or barrels.
- Rubbery – The odor of rubber, associated with very low-acid wines or excess sulfur.
- Stagnant – A stale water odor.
- Stemmy – Bitter, green odor of grape stems.
- Wet cardboard – A papery chemical odor usually associated with cork taint (TCA) or the misuse of filter pads or materials.
- Yeasty or leesy – The odor of yeast that may develop if dead yeast cells remain in contact with the wine too long. May be normal in some sparkling wines or those aged “on the lees”.
- Reduction or reductive – A term referring to the smell of rotten eggs, garlic, struck matches, cabbage, or burnt rubber. Can occur in what is known as reductive conditions: (i.e., conditions that lack oxygen).