Wine spoilage refers to chemical or microbial changes that render a bottle unpleasant or undrinkable. Understanding the mechanisms behind these faults allows consumers to better preserve their purchases and identify when a wine has passed its prime. Degradation is often predictable, stemming from environmental factors or contaminants introduced during production or storage.
The Main Chemical Causes of Spoilage
The most common chemical fault is oxidation, occurring when wine is exposed to too much oxygen, often through a faulty seal or after opening. This exposure converts ethanol into acetaldehyde, a compound responsible for distinct off-flavors. Acetaldehyde imparts aromas described as nutty, bruised apple, or sherry-like, stripping the wine of its fresh fruit character.
Oxidation also changes the wine’s color as phenolic compounds react with oxygen. White wines deepen into a brownish-gold hue, and red wines take on a brick-orange rim. This chemical transformation is irreversible and progresses rapidly once protective sulfur dioxide levels are depleted.
Another significant chemical cause of spoilage is heat damage, often called “cooked wine” or maderization. Exposure to temperatures above 80°F (27°C) causes the liquid to expand significantly. This expansion can push the cork partially out, leading to seepage and allowing oxygen to enter, accelerating spoilage.
High temperatures fundamentally alter the wine’s chemical structure, causing delicate fruit esters and volatile compounds to break down. This results in flavors that taste jammy, stewed, or burnt, replacing freshness with a flat, caramelized character. The damage is cumulative, meaning repeated, short-term exposure is as detrimental as a single, prolonged heat event.
Recognizing the Signs of Spoiled Wine
Identifying a spoiled bottle begins with a visual inspection. A white wine that has turned deep gold or brown, or a red wine with a distinct orange or brick-colored rim, indicates significant oxidation. Cloudiness or haziness in a young, filtered wine can also signal microbial activity or protein instability.
The condition of the cork can provide a visual clue, especially if it is protruding noticeably or if sticky residue is visible around the foil. These signs suggest the wine was exposed to excessive heat, compromising the seal and allowing air to enter.
Aromas provide the most definitive evidence of spoilage, often presenting as distinct off-odors that mask the intended fruit profile. Smells resembling vinegar or nail polish remover point toward volatile acidity. A musty, damp basement, or wet cardboard smell is the signature of cork taint.
The absence of fruit aroma, replaced by a flat, nutty, or burnt sugar smell, confirms heat damage or advanced oxidation. The taste test reveals a lack of freshness, excessive bitterness, or a sharp, overly sour profile that is unbalanced and unpleasant.
Microbial and Cork-Related Faults
Beyond chemical degradation, specific microbial and cork-related faults can render a wine undrinkable. Cork taint, caused by 2,4,6-trichloroanisole (TCA), is introduced by contaminated corks, not poor storage. TCA imparts a distinct aroma of damp basement, wet dog, or moldy newspaper, flattening the wine’s fruit character.
Another common microbial issue is volatile acidity (VA), primarily caused by Acetobacter bacteria converting ethanol into acetic acid and ethyl acetate. This process results in the sharp, pungent smell of vinegar or, in higher concentrations, the odor of nail polish remover. While low VA can add complexity, excessive levels are considered a fault.
The yeast Brettanomyces is responsible for a fault often called “Brett,” which produces aromas described as barnyard, band-aid, or medicinal. This yeast thrives in winery environments. High concentrations overwhelm the wine’s natural flavors, making it taste rustic and unbalanced.
Best Practices for Wine Storage
Preventing spoilage relies on maintaining a stable environment that minimizes risk factors. The most important factor is temperature control, ideally keeping wine between 50°F and 59°F (10°C and 15°C). Consistency is paramount, as rapid or frequent temperature fluctuations stress the cork seal and invite oxidation.
Wine should be stored in a dark location, as ultraviolet light can trigger chemical reactions leading to “light-struck” flavors, often described as smelling like wet wool or burnt rubber. Minimizing vibration is also beneficial, as constant movement can accelerate aging and disturb natural sediment.
For bottles sealed with natural cork, storing them horizontally ensures the cork remains in contact with the wine. This prevents it from drying out and shrinking, which would allow air ingress. Maintaining a moderate humidity level, ideally between 50% and 70%, helps keep the cork moist and pliable.
Once a bottle is opened, the remaining wine immediately begins to oxidize, requiring specific preservation techniques. Re-corking and refrigerating the bottle slows the chemical reaction significantly. Using a vacuum pump or inert gas system can physically remove or displace the oxygen, extending the wine’s drinkability for several days.