We have all had wine we didn’t like. The reason for our dislike may be subjective, but it could also be due to a faulty wine. In this article, we’ll explore some of the most common wine faults.

Corked wine (cork taint)

Corked wine is caused by the chemical TCA (2,4,6-trichloroanisole), mainly owing to microbial contamination of the cork. In the most obvious cases, the wine smells like wet cardboard or wet dog, and most people can spot it right away. If it’s marginal, the wine lacks a pleasant, fruity aroma and there is no aftertaste at all. Unfortunately, a lot of people blame corked wine on the winemaker, but he is actually the victim.

Around 10 to 15 years ago, it was estimated that 5–7% of wine had cork taint, and this is the reason the screw-cap closure was developed. Cork producers have tightened their quality control, and hopefully the percentage of corked wine will now be significantly less. While corked wine is not harmful, it negatively affects the wine’s characteristics and should be rejected. However, don’t confuse corked wine with the tiny, innocent bits of cork that sometimes float in wine.


Caused by excessive contact with oxygen during the winemaking or storage process, the telltale sign of oxidation is a lack of brightness, both in appearance and nose. Oxidised red wine is brick-orange red and oxidised white wine has a brownish tint. The fresh, fruity aroma is replaced by bruised apple, honey and, in the worst cases, soy sauce and vinegar. If the wine is fresh off the shelf or from a restaurant, you should return it. If it is a by-the-glass wine, you should ask the server when the wine was opened. Depending on the wine quality, it can be kept fresh in the fridge for one or two days.

Wine that’s over 10 years old is likely to show some oxidative characteristics, but these should not be too intense. However, not all wines are meant for ageing. Over 90% of the wine on the market is made to be enjoyed within 3–5 years, and if you keep it for too long, it will pass its peak time of enjoyment and show every sign of fatigue.


Reduction is the opposite of oxidation, when a wine is exposed to too little oxygen in order to preserve its freshness and fruitiness. A mildly reductive wine often smells of gun flint, smoke and struck match, adding complexity to the wine that’s actually liked by many consumers. However, it if is too reductive, the wine will smell like rotten egg or boiled cabbage. Sometimes these unpleasant aromas, caused by sulphur compounds, may be blown off if the wine is exposed to air after pouring it into a glass. If this doesn’t occur, the wine is clearly faulty.

Heat damage/cooked wine

High temperatures hasten chemical reactions, and if a wine is left in a high-temperature environment for a prolonged period of time, such as in a car boot or under sunlight, it will taste jammy and like stewed fruits, without any freshness, and it will likely have oxidation characteristics.

Brettanomyces (Brett)

Brett is a yeast that thrives in unhygienic cellars and finds its way into wine. It grows if a wine has a high pH, low sulphur dioxide or is stored in warm temperatures. It adds aromas such as bandage and animal to wine and, at the same time, dulls the fruitiness. In the right quantity, it can increase the complexity of a wine, but at a high level, the wine may develop farmyard aromas and even a mousy nose that is off-putting.

Brett is highly subjective. It is actually a signature for some famous wineries and many consumers fall for it. Australian winemakers have zero tolerance for it, and even a whiff of brett is considered a faulty wine. Funky natural wine is often laden with brett aromas.

Volatile acidity (VA)

VA is another microbiological spoilage, this time caused by bacteria that smells like acetone or nail varnish. To a certain extent, all wine has volatile acidity. It is one of the winemaker’s tools to add “high-toned” notes and bring complexity. Like brett, it is pleasant at low levels, but too much will tip the smell to downright vinegar and the wine will taste sour.

Harmless wine diamonds and sediment

Sometimes we may find precipitates in a wine when we pour the last few glasses. These are actually harmless. In white wine, there can be crystal-like substances that may be mistaken as pieces of broken glass. In fact, they are only tartrate deposits that occur when the wine is stored in a cold environment for a long time. In red wine, tannin and colour molecules bond to each other. Over time, these molecules become too big and fall out eventually, resulting in sediment that is common in aged wine. However, we may also find them in unfined and unfiltered young red wine. Fining and filtering are processes that polish wine, but they may also remove flavour and texture. Quality-conscious winemakers, often producing only in small quantities, do not fine or filter their wine in order to preserve the integrity.

The next time you have a bad wine at a restaurant, try to pin down the unpleasant nose. If it is corked or cooked, ask for a second bottle. If it is reduced, see if it improves after exposing it to air. For oxidised, bretty and high-VA wine, since the issues come from winemaking, unfortunately the second bottle is likely to be just as bad.

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A marketer turned winemaker, I make, promote, judge, write about and drink wine.

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