Corked Wine and Other Wine Defects

Sommelier tips on how to spot faulty wine

It was one of our wine exploration trips to Hungary. We ordered a nice bottle of Italian wine in a Budapest restaurant. My friend Kaoru, a sommelier from Tokyo, tastes the bottle and sends it back. The wine smells onion!

Wet dog, horse sweat, garlic, vinegar, rotten egg, cauliflower, cat pee – these are possible wine aromas too, or rather, they are wine defects.

The world of wine defects is fascinating and diverse. Wine scientists analyze wines to understand the source of the faults, which include not only the smell but also colour, transparency and taste. 

Defects can be caused by accidents in winemaking, under-ripe grapes, human errors, diseases, microorganisms and various contaminations. 

Wine faults are not always making the wines undrinkable. Most of the time, faulty wines are not harmful to us. However, nobody wants to drink wine with visible defects or smelling wet dog.  We all demand our wines to be of perfect color, brilliant, transparent, and to reflect the best aromas and palates. 

At the same time, we all consume a lot of flawed wines without even realizing it. Smell defects are much harder to detect than color defects. Sometimes, we don’t know what the faults are, often thinking that what we taste is an attribute of a particular wine style.  Even sommeliers get confused about whether the wine is faulty or the taste is intended.

Moreover, wine taints have been changing through time.  The proportion of faulty wines have been decreasing as a result of improvements in sanitary conditions at wineries, investments in temperature-controlled equipment and facilities, and healthier vineyards, as more sustainable farming and biodynamic methods have been introduced. However, in the last 15 years, scientists detected new defects in juices and wines. 


Colours of faulty wines generally turn darker and more brown. This is true for both white and red wines. White wine may turn deep yellow, orange or brownish. Red wine may turn from purple or ruby to orange-brown. Wines turn colors prematurely as a result of oxidation, or too much exposure to air usually caused by a failure of the closure allowing oxygen to interact with the wine. You have probably seen red wine turning brownish when a bottle is left open for about a week. 

During my wine tours, we often see bottles from early and mid-1800. The wine in the bottles looks like it has almost completely lost its color, and looks light pink, orange and almost transparent.

Do not mix this change in color with similar changes in the normal ageing process, as micro-oxygenation occurs in cork-sealed bottles with the time.  For example, some 30-year-old Bordeaux wines are perfectly good to drink, even though the color has turned  orange-brownish. 

Also, some wines are made in oxidized style and are intended to show deeper and brownish colors.  For example, wine from Vin Jaune (golden wine) from the Jura region in France. These wines are intentionally aged in contact with air.  In this case, wines can be perfectly good.

However, when younger wines turn brown quickly, there is a problem.  For example, a 2015 bottle of Cabernet Sauvignon should still be bright ruby color.

Oxidation will affect not only color, but also the wine’s taste and smell giving wines aromas of toffee, honey or caramel.  Oxidized wines will lack freshness and fruitiness.

Wine preservation tools like Coravin can be used to prevent oxidation in the bottles that have been opened.  They keep oxygen away from the wine for a few months or even years by replacing oxygen with argon gas.


Wine can develop sediments,  haze or unwanted CO2.  Deposits can be natural and come from the winemaking process.  Haze can be of metallic nature: ferric, cupric or of colloidal nature: proteic and tartaric. 

Deposit in older reds and tartaric deposit (transparent crystals) in whites are normal and not harmful. Just filter them out or use a decanter. 

Wine can get bubbles of carbon dioxide as a result of unexpected secondary fermentation in a bottle, a winemaking error or a lack of sulfites which help to stabilize the wine.  Slight effervescence is normal in some wines like Portuguese Vinho Verde, Italian Moscato D’Asti or Italian Bonarda, but not expected in dry reds.

Sometimes wine may appear oily. This is the result of the development of spoilage lactic acid bacteria.

The taste of the wine can also be affected, it is probably better to discard the bottle.


In faulty wines, the smell can be unpleasant, however, it does not have to be. If the smell is  not an expected smell for the style of wine or a smell that hides/masks wine typicality, it is considered to be a defect. A wine that lacks fruitiness and becomes bland is faulty.

Wrong smells that can be caused by various processes including:

  • UV light damage, sunlight reacting with sulfur compounds and other wine natural compounds
  • excess of sulfur dioxide from spraying 
  • inadequate and contaminated cork
  • fermentation errors
  • “dirty” yeast

Here are some possible reasons for some wine odors

Wine DefectPossible Cause
rotten apple
nail polish remover

oxidation, air in the bottle,
boiled cabbage
rotten egg
blocked drains
excess sulfur on grapes
fermentation problems
stuck fermentation
lees of poor quality
horse sweat
sticky plaster
hot vynil
smoked meat
spoilage yeast (brettanomyces or Brett)
freshly cut grass
under-ripe grapes
bad de-steming
earth and/or mushrooms
rotten grapes
mold on grapes
acacia blossom
curry, rancio
poor protection against oxidation
cork of poor quality
dirty ash tray
camp fire or burnt
smoke taint
sulfurexcess of sulfur dioxyde
soapbad management of fermentation
wet cardboard
cork taint

Cork taint along with brett are some of the most common defects. 

Cork taint is caused by a chemical called trichloroanisole or TCA which develops as a result of treatment of some fungi with chlorinated phenolic compounds.  Not only cork stoppers are responsible for taint, but also wooden barrels, storage conditions and the transport of corks and wine. Even screwcap wines can be contaminated with TCA at a winery.

Corked wine appears in up to 7% of wines. Recently, this percentage has been declining as cork producers have invested considerable sums in developing treatments. Amorim, a Portuguese cork producer, patented an NDTech cork screening technology that rejects TCA levels higher in proportion than one drop of water in 800 Olympic size swimming pools.

Unfortunately, in most cases, there is nothing much you can do with faulty wine other than return it to the seller.

To train yourself in the identification of wine faults, you can use a faulty aroma kit by the French company Le Nez du Vin (The Nose of Wine). Sommeliers use it to train themselves.  Also, guessing wine aromas proved to be an excellent wine party idea. Surprisingly, cauliflower aroma smells the worst to me. 

Happy tasting!

My selection of Champagne

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