Most of the time, it is really not your fault. Although, like all wine lovers, we are to bear the consequences. There is no universal % on how many faulty bottles of wines are out there. Just as a reference, cork taint – one of the most notorious faults – is widely believed to affect 2 to 3 % of all bottled wines in the world. (Back in early 2000s, the figure is as high as 7 to 8%.)

Generally, oxygen, micro-organisms, and uncontrolled level of chemical reactions trigger the most common wine faults. Instead of presenting this subject from a narrative cause-and-effect account, we are going to do it the other way round in this blog.

Below is a list of fault-related aromas (effects) of which most wine lovers would happily avoid than welcome when uncorking a bottle of wine. If you do unfortunately encounter one, or more, of the below aromas in your bottle, let us tell you why (causes) the bottle shows that way.

“I smell sherry-like salty tang, and a bit of vinegar, nail polish remover notes in the wine…”

Culprits: Oxygen, Volatile Acidity

Oxygen: A friend and a foe

As a friend, it keeps fermentation going and when judiciously used (for example, microoxygenation during maturation), it specifically enables red wines with a lot of tannins and density to soften and become more approachable at a younger age. As a foe, the chemical reaction between oxygen and oxidisable molecular compounds can eventually strip the wine of pleasant aroma compounds. At an intermediate stage, the wine’s primary fruit aromas will fade away and start to show Fino-like salty tang (technically known as acetaldehyde). On the palate, an unpleasant sensation of bitterness starts to build. As the wine becomes fully oxidized, it will be completely stripped of any fruit qualities and resemble vinegar entirely.

Oxidation and Volatile Acidity

When oxidation as an issue happens, one will concurrently get a buildup of volatile acids that may go out of control eventually. Volatile acidity comes in two forms: Acetic acid (smell like vinegar when in extreme form) and Ethyl Acetate (smell like nail polish remover when in extreme form). During the winemaking process, warmer temperature fermentation – be it during primary alcoholic fermentation, or malolactic fermentation – both provide for an environment that encourages acetic acid formation.

What’s really causing all the trouble here is this little guy called acetobacter, which is a micro-organism (bacteria) naturally found in high sugar fruits and flowers. If not properly controlled, acetobacter can work efficiently with oxygen in a warmer temperature environment to break down ethanol (alcohol) into acetic acid. Ethyl acetate (which smells like nail polish remover at a high concentration) is the lovechild of ethanol (alcohol) and acetic acid. (For the geeks, when 5 to 10 parts of acetic acid is formed, 1 part of ethyl acetate will be produced.)

At which level and how things get out of hand?

When acetic acid is kept at an acceptable level (usually no more than 0.5g/L in a clean young red wine) and ethyl acetate at no more than 0.1g/L, they positively influence the wines by elevating a wine’s fruitiness. Human nose can detect acetic acid at 0.5g/L and ethyl acetate at 0.08g/L. It is when these values triple our detection threshold that things are considered getting out of hand.

Oxidized wines and wines with high volatile acidity can be a product of not-so-ideal winemaking management; as much as it can be a result of unsatisfactory cellaring after bottling. Wines under natural cork, if not stored properly, will become susceptible to oxidation risk. And you have heard it many times just now already, oxidation and volatile acidity are very much “brother from another mother”.

A fault or a style?

On a last note, it is worth mentioning that although a wine should normally not smell oxidized nor sherry-like, there are indeed very specific wine styles that are intentionally made to be oxidative such as Gran Reserva white wine from Rioja (an extreme yet stunning example being 1986 Marques de la Murrieta Rioja Blanco Gran Reserva Especial – having spent 252 months in American oak barrels). Same goes with Sherry, which is deliberately made to feature a savoury, tangy taste profile or oxidative, nutty style. Bold play of volatile acid level is a marker of traditional style Italian wines – who wouldn’t remember the classic profile of Chianti, with lifted tart red fruit, sundried tomato tones?

“The wine smells musty, like moldy cardboard…”

Culprit: Cork Taint (2, 4, 6-Trichloroanisole)

The layman term “cork taint” puts the blame entirely on corks, whilst the problem of 2, 4, 6-trichloroanisole (TCA) actually roots not only from corks, but also unsanitary barrels and any sources of “tainted” wood within the winery. Human nose are incredibly sensitive to TCA, whilst our detection threshold for acetic acid is 0.5g/L, that of TCA is at 2 parts per trillion. (0.000000000002g/L).

What causes cork taint?

The two agents at work that produce cork taint are chlorophenols (an industrial pollutant created when chlorine is first used to sterilize and bleach wood) , and wood-eating fungi. The latter metabolizes and converts chlorophenols into TCA. These remain in oak trees and get transferred into the final product: the natural wood corks themselves. Contact with wines cause TCA to dissolve and impart damp basement, musty, moldy cardboard characters in wines.

It is believed that the issue of TCA global wine industry costs the world more than US$10 billion a year. Specific solution such as use of peroxide instead of chlorine to sterilize and bleach corks; to alternative closures such as Stelvin closure (screwcap), sythentic (plastic) corks and glass corks do alleviate the issues.

Is cork taint bad for health?

The burning question among wine consumers are: Is TCA toxic? Despite the source partly being an industrial pollutant, TCA is actually harmless to human body. It simply significantly reduces the pleasure of wine enjoyment as it strips the wine of positive aromatic attributes.

Can I remove cork taint?

In fact, there is a scientifically sound remedy to cork taint. Essentially, it involves pouring your bottle of corked wine into a container lined with cling film. The scientific logic behind it is that TCA molecules of neutral charges will be drawn and attracted to the cling film, as they are chemically alike. This theoretically remove TCA molecules from the wine and makes it drinkable again. We have heard a few collectors trying this method out to different degrees of success – tell us your experience!

“It smells like barnyard, horse sweat, manure… simply funky”

Culprit: The yeast strain Brettanomyces

Brettanomyces (Brett) is considered an agent boosting complexity in wines until when things get out of control. Rather like salt in food, it is nice until when you get too much of it. In Asia, we celebrate a diverse range of savoury qualities (umami, kokumi, fermented flavours) in our cuisines. Along that line, it does appear to heighten Asian drinkers’ tolerance of Brett-derived aromas than Western counterparts.

Hello Geeks, Brett comes in three forms…

Brett is a yeast naturally found in the winery environment, and they produce 3 forms of volatile phenol compounds, in abbreviation, 4-EP, 4-EG (which gives band-aid, barnyard characters) and 4-EC (which gives horsesweat, cheese-like characters). These phenol compounds exist in different ratios in our favourite grape varieties like Pinot Noir and Cabernet. At an acceptable ratio, these combinations add complexity in the form of pungent spices, leather notes to wines. Brett as a yeast is known to be most active in between primary alcoholic fermentation and malolactic fermentation.

A fault or a style?

Global warming (thus likelihood of higher pH in wine) and the trend of minimal use of sulphur dioxide both encourage Brett activities during winemaking. Acceptable level of Brett tend to impart an impression of “complexity” in wines. Though when it spirals out of control, it tends to strip the wines of all aromas except overt rustic barnyard, band-aid notes; and leave the wine tasting metallic and drying on the finish.

Ultimately winemakers have various way to manage Brett influence, going from pH management (closely related to harvest timing) to winery hygiene (fermentation temperature and SO2 usage). It is all a matter of balance at the end of the day – Brett is a perfect case illustrating the effects of “Salt Theory” for wine lovers.

Different detection threshold?

Human detection threshold for Brett-derived compounds are somewhere in between our detection threshold for volatile acidity and TCA. Humans can pick up on Brett notes so long as the phenol compounds exist roughly at 0.0003g/L. When more than one form of Brett exists, our detection threshold tends to lower. What makes Brett a little too much? Australian Wine Research Institute (AWRI) studies show that when Brett exists, in one single phenol compound form say 4-EP, at more than 0.0006g/L it is considered dominant enough to turn wine consumers off.

Leaving all the data and science aside, it is worth noting that detection threshold vary depending on each persons’ sensitivity to certain smells and their cultural (and thus culinary) exposure. Acquired knowledge also plays a part in lowering detection threshold, meaning that you may find yourself much more aware of faults after a wine fault training. There goes the old saying – “Ignorance is bliss”.