Julie Harrison - Faults in wine

Sometimes you taste a wine and it isn’t quite right.  Whilst it doesn’t happen that often there are faulty wines that do get onto the shelves.  A few of the more common problems are detailed below.

Oxidation of wine is a fault and  is the result of the same process that you see when you leave a cut up piece of apple on the bench.  Wines do not like too much oxygen exposure and the result is a wine that is dull and nutty in flavour.  The wine may taste a bit like a Sherry and in fact controlled oxidation is an important part of Sherry and Tawny Port production.   It is pretty easy to spot  by looking at the wine colour.  Reds turn a brick colour and whites become gold brown or amber. Oxidation is often  due to a faulty cork letting too much air into the bottle.  You can smell and taste it clearly if you leave a bottle of wine open too long and it is something to look out for when you buy wine by the glass at a bar or restaurant as there is the possibility that the bottle has been open for a while.  

Occasionally you may come across a wine that has a rubber or rotten egg smell to it.  In this case the wine is described as being reduced, which is the opposite of being oxidised.  Sulphur compounds can be a produced by yeast during fermentation.  Despite painting oxygen as “wine enemy number one”, small amounts are necessary at certain stages of  the winemaking process to combat this.   If you come across a wine that you suspect is reduced adding a copper coin to the glass should fix the problem as the copper mops up the smelly molecules, alternatively decanting the wine may help.

Another common wine fault is  “cork taint.”  This has been largely eliminated in New Zealand with the advent of the screw cap but you can still come across it in older wines or wines from other parts of the world.  It occurs when wine comes in contact with a chemical referred to as  TCA (2,4,6-trichloroanisole) and most often a contaminated cork is responsible, although it can come from contaminated wood chips, barrels or other winery wood.  TCA is not a health risk but at is detectable at very low levels (10 parts per trillion).  At low levels it can make a wine seem dull  but as levels get higher the wine becomes undrinkable.  It is believed that individuals vary in how sensitive they are to TCA with some people being able to detect minute amounts  with others not noticing even quite high levels.  Look out for the smell of mould, wet cardboard and damp cellar.  Just how common cork taint is depends on who you are talking to but a general consensus is that you  see it in around 3% of wines.

Yeast and bacteria  are part of winemaking but sometimes unwanted bugs get involved one of these being the yeast Brettanomyces, commonly called “Brett”. Funnily enough winemakers sometimes do not mind a bit of Brett contamination as at low levels it adds complexity and gives an earthy character to the wine.  It is responsible for the sweaty saddle character you get in some Australian Hunter Valley Shiraz.   However when it causes the wine to smell of rotten meat or the inside of a band aid box it is not quite so desirable.  Acetic acid bacteria can be responsible for high Volatile Acidity in a wine.  This is when too much acetic acid or ethyl acetate is formed in the wine and you get vinegar taint or nail polish remover character.  Excessive use of Sulphur dioxide may impart a struck match character to the wine.   Don’t worry about finding crystals in your wine bottle.  These tartrate crystals have naturally fallen out of solution, are harmless and do not impact on the quality of the wine.