Common Wine Faults and How to Detect Them

There are several common wine faults in wine such as oxidization, Volatile Acidity and Brettanomyces infection, which can be easily identified when you know what to look for. Below we will run over some of the common wine faults and how to identify them.

Oxidization

This is one of the most common wine faults and will occur, generally, in older wines. It is a result of too much exposure with oxygen. Whites are most susceptible to this fault as they lack the antioxidant, tannin, that red wine has.

It can be characterized by the wine becoming a brownish-orange color. The nose will be dull and lack freshness and aromatics. The palate will also be dull and dry, leaving an unpleasant after taste much like that of a slice of apple that has sat on the bench too long. The wine is not toxic but it is not pleasant to drink and should be destined for the kitchen sink.

Here are some key causes:

Preventing oxidization: Oxidized wine is certainly not something you want in your wine, but thankfully it's easy to prevent if the right steps are taken. If you crush your own grapes, try to keep the temperature below 50F (10C) up to the point where your yeast is pitched. Keeping the amount of racking you do to a minimum is another easy option. When bottling, recharge the wine with free SO2 and use good quality closures.

Proper Storage: Storage for wine must be kept at a constant temperature preferably at 53-64F (12-18 C). If stored in an area with high temperature fluctuations the oxygen in the ullage (the space between the wine and the cork) will expand and push the cork out of the bottle slightly when the bottle cools the cork will retract and suck fresh oxygen into the bottle. When this happens repeatedly over a long time the wine will oxidize.

Volatile Acidity

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Volatile acidity (also known as VA) is a high level of Acetic Acid in a wine. A wine with VA will come across as vinegary. VA can occur in a wine via various means:

  • Wine grapes were of a poor quality, such as split skins or disease
  • Too much exposure to oxygen
  • Lack of Sulphur Dioxide (SO2)

When the skin of a grape is split it exposes the juice to yeasts, naturally living in the air and on the grape skins and results in a higher population of acetic acid bacteria.

When these grapes are crushed and fermented the resulting wine will have a higher than usual amount of acetic acid. Acetic acid bacteria requires oxygen to grow and as a result the more racking and transferring of wine in the winemaking process can increase the amount of acetic acid bacteria growth, this can be avoided by transferring only when necessary and having a good level of sulphur dioxide to protect against oxygen.

While acetic acid itself may be difficult to detect Ethyl Acetate is the product of ethanol and acetic acid and can be detected by the scent of glue or nail polish remover. Again the wine will not be toxic but is unpleasant to drink.

If you're concerened about having enough free SO2, a super rough guide (as it changes from grape to grape) is 1 tablet per gallon (1 tab per 4 liters). Add it to the juice then wait 24 hours before inoculating, as yeast will struggle to ferment with sulphur dioxide present. You can then add another 1 tablet per gallon before bottling.

Cork Taint (TCA)

cork taint wine faults

Cork taint is the presence of 2,4,6-trichloroanisole in wine and often is introduced via corks that haven’t been properly cleaned in the cork making process. It can be characterized by a scent of wet newspaper or wet dog. The wine itself will be dull and again undrinkable but won’t kill you.

Brettanomyces Infection in Wine

Brettanomyces is a genus of yeast which is often referred to as ‘brett’ and is most commonly a result of unsanitary winemaking practices such as uncleaned equipment and barrels.

While in beer it can be added as a desirable component, in wine it is referred to as a ‘yeast spoilage’ as it adds flavor altering characters to a wine. Once in your winemaking space, it's incredibly difficult to get rid of. There are stories of wineries burning thousands of dollars of oak just to get rid of it.

It can sometimes be confused with TCA as it can come across as a damp, barnyard type of scent but can also be detected by aromas of band-aid or antiseptic and can leave a cloying, coating sensation in the mouth. Some winemakers will argue that small amounts add character to wine but in Australia it is viewed as a fault regardless of the concentration.

Grape Diseases such as Bunch Rots

bunch rots wine faults

There is a myriad of fungi that can cause havoc in the vineyards and winery, grey mold, powdery mildew, ripe rot just to name a few. Healthy fruit is always desired for winemaking, but sometimes in bad years it is unavoidable. The wine will appear dirty or ‘grubby’ on the nose and palate and often show earthy or mushroom like characters.

Common bunch diseases are powdery mildew, downy mildew and grey mold. Powdery Mildew is a fungal disease and can be identified by an ash like substance covering the grapes, it will scar and shrivel grapes causing low yields. Downy Mildew is a fungal disease and will appear as a grayish color on grapes, if left untreated the berries will drop from the bunch. Grey mold (or Botrytis) is a fungal disease that causes grapes to shrivel, and become very high in sugar and volatile acidity. Split bunches commonly occur when grapes have been over-watered and will cause the grape skin to tear.

Re-fermentation After Bottling

This occurs when a wine is bottled before it is stable and yeast cells re-ferment remaining sugar in the bottle. This causes a still wine to have CO2 and become fizzy. This can be detected if you open a bottle and it fizzes or is spritzy on the palate. This can sometimes indicate an infection as well.

Above are the most common wine faults, there are many more such as light-strike (overexposure to ultraviolet light, detectable by aromas of wet cardboard), DMS (Dimethyl sulfide, characterized by vegetal notes such as boiled cabbage) and heat damage. Wine faults are different to wine flaws such as over ripeness, under ripeness and over oaking etc.

by Jack Davis
Jack has 12 years worth of experience in the wine industry. He became an avid homebrewer after picking up home winemaking as a hobby a year ago. When he's not making wine, he helps judge at local wine competitions.

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written by Jack Davis

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