FAULT	SUBSTANCE	SMELLS LIKE	COMMON CAUSES	MICRO-ORGANISM	MOST LIKELY WINES AND COMMENTS
Sulfides (H2S)	Hydrogen sulfide Mercaptans Dimethylsulfide (DMS)	Boiled eggs Onion, garlic, burnt rubber Tinned corn, cooked vegetables	Lack of amino acids (nitrogen) in fermenting juice or must. Can be avoided by the addition of Diammonium Phosphate during fermentation	Saccharomyces sp. (yeast)	All, particularly reds. At very low concentrations may add to complexity, but rarely beneficial.
Brettanomyces	4-ethyl phenol 4-vinyl phenol	Band-aid, horsey, barnyard, “sweaty saddle” spicey	Low SO2 Elevated storage temperatures. Infection during barrel storage.	A wild yeast strain. Brettanomyces sp.	Only reds, particularly those stored in second use barrels. Also, more common in deeply coloured red wines. Can add to wine complexity if subtle.
Mousy Taint	Aceyltetrahydro- Pyridines	Mouse urine Corn chips Jasmine rice	Low SO2 High pH wines	Lactobacillus brevis	Reds and particularly fortified wines as these tend to be high in pH and are stored in barrels for extended periods. Sometimes difficult to detect by smell but intensifies in mouth after spitting. Can be accompanied by a strong metallic bitterness.
Volatile Acidity (VA)	Acetic acid	Vinegar	Ullaged barrels or tanks. Damaged fruit. Low SO2 Poor winery hygiene.	Acetobacter sp.	All, never beneficial. Gives the palate a hard and hot mouthfeel.
	Ethyl Acetate	Nail polish remover or solvent.			All. In reds considered acceptable at low levels. An accepted part of botrytised wine styles.
Oxidation	Acetaldehyde	Sherry Brown apple Papery flavour	Low SO2 during winemaking. Low SO2 and high dissolved oxygen at bottling.	None	All, particularly light bodied whites. In whites mostly accompanied by a brown hue.
Sulfur Dioxide	SO2	Struck match	Excessive addition particularly at bottling.	Can also be produced by Saccharomyces yeast during ferment.	Whites, particularly light bodied. Rarely seen in reds as the SO2 is mostly bound to red pigments.
Cork Taint	2,4,6 Tri-chloroanisole	Musty	Sealing with cork. Storage in musty barrels.	Moulds esp. Aspergillus sp.	Can affect any wine sealed with a cork. Easier to perceive in whites and sparkling wines.
	Geosmin Octenol Methylisoborneol	Earthy Mushroom Compost	Sealing with cork. Storage in musty barrels.	Moulds esp. Aspergillus sp.	Rarely encountered. All styles, but may seem a ‘natural’ aroma in reds.