The Science of Wine Faults: Identifying, Understanding, and Appreciating the Complex World of Wine Flaws

For experienced wine connoisseurs, there’s nothing more disappointing than opening a prized bottle only to discover it’s “off.” Yet, the realm of wine faults is far more nuanced than simply labeling a wine as flawed or spoiled. Some faults are clear-cut, like cork taint or oxidation, but others can walk a fine line between defect and desirable character—think of the smoky notes from Brettanomyces or the sherry-like tang of slight oxidation in an aged white Burgundy. This in-depth guide will explore the chemistry, sensory impact, and even the unexpected allure of wine faults. By the end, you’ll have a more sophisticated understanding of what makes a wine flawed, and in some cases, how certain flaws can actually add complexity and depth.

What Are Wine Faults?

Wine faults are undesirable characteristics that develop during grape growing, winemaking, or storage. These faults are caused by chemical compounds that produce off-flavors, aromas, or visual defects. While some faults render a wine undrinkable, others can contribute unique attributes that might be appreciated in certain contexts or styles.

The Fine Line Between Fault and Flavor

One of the most intriguing aspects of wine faults is that they are not always universally negative. Some faults, in low concentrations, are integral to the identity of specific wine styles. For example, the “barnyard” aroma from Brettanomyces is considered a flaw in most wines but is cherished in certain Rhône reds and Burgundian Pinot Noirs. Similarly, the oxidative notes that would ruin a young, fresh Sauvignon Blanc can add a complex nutty quality to a well-aged white Rioja.

The Top Wine Faults: Causes, Detection, and Impact

Let’s delve into the most common wine faults, exploring their chemical origins, how they manifest in the glass, and what they mean for the wine’s overall profile.

Cork Taint (2,4,6-Trichloroanisole – TCA)

• Cause: Cork taint is caused by the presence of 2,4,6-trichloroanisole (TCA), a compound that develops when naturally occurring fungi in cork react with chlorinated cleaning products or pesticides.
• Detection: TCA imparts a musty, damp cardboard or wet newspaper aroma, masking the wine’s natural fruit flavors and making it seem dull and muted.
• Threshold: Even at levels as low as 2-5 parts per trillion, TCA can devastate a wine’s profile. Its impact is cumulative, making it one of the most insidious wine faults.
• Should You Tolerate It?: Absolutely not. Cork taint is universally considered a major fault that ruins the wine.

Oxidation

• Cause: Oxidation occurs when wine is exposed to too much oxygen, leading to the formation of aldehydes. This can happen during production, aging, or improper storage.
• Detection: Oxidized wines often exhibit nutty, sherry-like aromas, accompanied by a loss of fresh fruit character. Whites turn a deeper golden color, while reds develop a tawny hue.
• Should You Tolerate It?: It depends. While young wines should never show signs of oxidation, controlled oxidation can be desirable in aged whites like Burgundy, Vin Jaune, or sherry.

Brettanomyces (“Brett”)

• Cause: Brettanomyces is a wild yeast that thrives in cellars with poor hygiene or in wines with low sulfur levels. It produces volatile phenols like 4-ethylphenol (barnyard, horse sweat) and 4-ethylguaiacol (smoke, clove).
• Detection: Depending on concentration, Brett can add intriguing complexity or overwhelm a wine with pungent aromas reminiscent of band-aids, leather, or manure.
• Should You Tolerate It?: This is subjective. A hint of Brett can add character to certain styles, particularly old-world reds. However, at high levels, it’s considered a fault.

Volatile Acidity (VA)

• Cause: Volatile acidity is primarily caused by acetic acid bacteria converting alcohol into acetic acid and ethyl acetate, often due to poor hygiene or excessive oxygen exposure.
• Detection: VA imparts aromas of vinegar and nail polish remover, and it can make the wine taste sharp and unpleasant.
• Should You Tolerate It?: A small amount of VA can lift the aromatics in robust reds or dessert wines, but high levels are undesirable in any context.

Reduction

• Cause: Reduction results from a lack of oxygen during winemaking or aging, leading to the formation of sulfur compounds like hydrogen sulfide (rotten egg) or mercaptans (burnt rubber, garlic).
• Detection: Reduced wines smell of rotten eggs, burnt matches, or rubber. Some milder forms of reduction may present as earthy or smoky notes.
• Should You Tolerate It?: Mild reduction can sometimes “blow off” with aeration, revealing a clean, complex wine underneath. If the odor persists, it’s a flaw.

Lightstrike

• Cause: Lightstrike occurs when wine is exposed to UV light, causing a reaction between amino acids and sulfur compounds. This is especially problematic in clear or light-colored bottles.
• Detection: Wines affected by lightstrike develop a distinct smell of cooked cabbage, wet wool, or skunk.
• Should You Tolerate It?: No. Lightstrike is an irreversible flaw that severely compromises the wine’s quality.

Mousiness

• Cause: Mousiness is caused by the presence of lactobacillus bacteria, which produce ethyl carbamate. Unlike most faults, mousiness is not detectable by smell but only by taste.
• Detection: It appears as a distinct aftertaste of mouse cage or stale cereal, often lingering on the palate. The phenomenon is more noticeable when the wine is warmer and less acidic.
• Should You Tolerate It?: Absolutely not. Mousiness is one of the most off-putting wine faults and is unacceptable in any context.

Advanced Wine Faults: The Gray Areas

While the above faults are typically considered deal-breakers, some defects can be more ambiguous, adding to a wine’s complexity when present in the right context. Let’s explore a few of these gray-area flaws:

Micro-Oxidation: A Controlled Fault?

Micro-oxidation is a technique used by winemakers to introduce small amounts of oxygen to soften tannins and enhance aromatic development. While this can add complexity, it can also push a wine dangerously close to becoming oxidized. An expert palate is required to discern whether a wine’s oxidative notes are intentional or the result of mishandling.

High Sulfur: Fault or Winemaking Choice?

Sulfur dioxide (SO2) is commonly used as a preservative, but excessive use can impart a pungent smell of struck matches or burnt rubber. While some winemakers argue that a little sulfur is preferable to bacterial spoilage, natural wine advocates reject its use altogether. The debate continues, but in most cases, sulfur aromas should dissipate with decanting.

Lactobacillus: Creating Funk or Flaw?

Lactic acid bacteria are crucial for malolactic fermentation, but uncontrolled growth can lead to spoilage, producing faults like mousiness or excessive VA. However, in controlled amounts, these bacteria can contribute to complex, savory flavors that some connoisseurs find intriguing.

Final Thoughts

For the discerning wine expert, understanding faults is not just about avoiding spoiled bottles—it’s about knowing how and when these flaws manifest, appreciating their impact, and sometimes even embracing them. As you deepen your exploration of wine, you may find that what was once considered a flaw becomes an integral part of the wine’s story and character. Ultimately, learning to navigate the world of wine faults will elevate your appreciation and expand your palate, allowing you to savor wine in all its unpredictable, complex glory. Cheers to embracing the imperfections!