When Wines go Bad (WineMaker)

Wine Faults

Whether you make wine at home, commercially, or simply enjoy drinking it, it’s likely you have encountered faulted wine; maybe it was the subtle aroma of geranium leaves, an aromatically muted glass pour, the unmistakable odor of barnyard, or 

perhaps you thought you poured yourself a glass of nail polish remover by mistake.

Whatever your experience may be, recognizing that wines reveal faulted characteristics for various reasons, each indicative of something that went awry in the vineyard, cellar, transportation, or storage period, is key to a more thorough understanding of winemaking.

There are many books and articles focused on exploring these faults in detail exhaustively, which is why this article will serve as a simplified, practical reference when searching for a rudimentary explanation of the most common faults.

Before we delve in, we must first understand the difference between a flaw and a fault. A wine exhibits any number of flaws when at some point in the winemaking process something was (or was not) done that led to the finished product exhibiting a feature not desired for the style or varietal. Wine flaws are minor issues, though the wine may still be entirely acceptable and even enjoyable. Flaws can be visual (tartrate crystals, sediment, haze, minor carbonation in a non- sparkling wine); aromatic (volatile acidity, sulfur dioxide, Brettanomyces, lack of- or non-varietal aroma, reduced sulfur compounds at low levels, diacetyl, over-oaking); or flaws of flavor (searing acidity, unintended sweetness, exceedingly high or abnormally low alcohol levels).

There is no incontrovertible point at which a flaw becomes a fault, though there are well-studied thresholds, the point at which we understand a wine’s fault to be unquestionably recognizable and/or overpowering of any other characteristics in the wine. Simply put, faulted wine is a flawed wine that has reached very high concentrations. When a wine entirely loses its typicity, and the flaw becomes the singular defining characteristic covering up any other aroma or flavor, the wine is faulted and considered undrinkable at this point. Here we will only cover some of the most common faults you are likely to experience through wine tasting or while making your own wine. Many of these can be co-created or stem from the same underlying issues, but for the sake of best understanding them at their core, each fault has been listed individually.


Though at times a purposeful and stylistic choice (such as in the production of Sherry with “oxidative characteristics”), oxidation occurs when oxygen and wine interact, creating recognizable oxidative aromas by modifying the wine’s chemical structure. Oxidation does not affect all wines equally nor in exactly the same way. For example, highly aromatic white wines will experience the effects of oxidation more readily and more obviously than tannic, phenolic-heavy red wines. Wine can become oxidized either before or after it is bottled.

Sensory threshold: Highly variable and dependent upon wine style. The line between “oxidative characteristics” and “oxidized wine” can be a matter of personal preference. 

Cause: Excessive oxygen exposure post-fermentation, extended maceration time with inadequate inert gas usage, insufficient free sulfur dioxide (SO2), bottling with faulty corks.

Detection: Diminished flavor and aroma. Aromas of stewed fruits, walnut, prune, fennel, hay, Sherry-like. Red wines become brick red/brown in color (particularly noticeable in young wine that began with rich red and purple hues), and white wines take on a darker golden or
brown hue.

Prevention: Sufficient use of inert gas, SO2, refrigeration, quality corks, and aging bottles on their side to prevent the cork from drying out. Using high-quality corks is important, alongside long-term storage in a cool, dark place, as heat accelerates oxidation and low humidity conditions will allow the cork to dry out.

Fix: Cannot be remedied. Prevention is key.


Acetaldehyde is the result of oxidized ethanol. It can be produced by acetic acid bacteria in low-oxygen, high-alcohol conditions. Yeasts can also convert ethanol to acetaldehyde in oxidative conditions.

Sensory threshold: 100–125 mg/L. Lower concentrations (70 mg/L) can impart fruity aromas, whereas higher concentrations (100+ mg/L) become objectionable. 

Cause: Film yeasts or Acetobacter in oxidative conditions, low SO2 levels, excessive headspace, faulty corks, adding excessive amounts of SO2during fermentation, high pH, and allowing fermentation temperature to spike too high.

Detection: Overall loss of varietal characteristics. Aromas of overripe or bruised apples, vegetal, dry straw, roasted nuts, almonds, and Sherry-like characteristics. Very high concentrations display metallic, sour flavors. White wines develop deeper golden or brown colors and reds acquire a brick red hue.

Prevention: Top up barrels to prevent excessive headspace. Be aware that increasing pH, fermentation temperature, and adding SO2 during fermentation can increase acetaldehyde levels. Minimize wine’s exposure to oxygen after fermentation. Maintain proper free SO2 levels.

Fix: Add SO2, which will bind to the acetaldehyde; however, this addition is merely temporary as the SO2 will eventually diminish, allowing the acetaldehyde to be freed.

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