The presence of fine bubbles or a slight prickle on the tongue in a still wine is often unexpected. This unwanted effervescence, or pétillance, occurs when carbon dioxide gas, which is normally allowed to escape during winemaking, becomes trapped in the sealed bottle. While sparkling wines are intentionally bottled under pressure to contain the carbon dioxide, its appearance in a bottle meant to be still indicates a deviation from the winemaker’s plan. Understanding the source of this trapped gas involves examining both biological processes and physical conditions.
When Yeast and Bacteria Wake Up
The most common biological reason for unexpected bubbles is a spontaneous secondary fermentation occurring inside the sealed bottle. This process happens when dormant yeast cells reactivate after bottling because they find residual sugar that was not fully converted to alcohol during the initial winemaking process. The yeast consumes these remaining sugars, creating small amounts of alcohol and, more importantly, carbon dioxide gas that causes the fizz.
Another biological cause is the unintentional onset of malolactic fermentation (MLF) post-bottling, which is driven by bacteria rather than yeast. MLF involves the conversion of tart-tasting malic acid, naturally present in grapes, into softer lactic acid. This conversion releases carbon dioxide as a byproduct. While MLF is deliberately encouraged in nearly all red wines and some white wines like Chardonnay to achieve a rounder mouthfeel, its unexpected occurrence in the bottle leads to unwanted effervescence.
These biological processes that lead to spontaneous carbonation indicate a stability issue in the wine but rarely pose a health risk to the consumer. The wine may taste flawed or different than intended, sometimes developing off-flavors like diacetyl (butter or butterscotch) from MLF. However, the presence of the yeast or bacteria itself does not typically render the wine unsafe to drink.
Temperature, Dissolved Gas, and What to Do Next
Sometimes the effervescence is not the result of microbial activity but simply the physical state of dissolved gas. All still wines contain a certain amount of dissolved carbon dioxide from the initial fermentation. Winemakers often leave slightly higher concentrations in young, crisp white wines to enhance the perception of freshness and acidity, a deliberate choice that can result in a slight, harmless prickle.
The solubility of carbon dioxide in wine is strongly affected by temperature; as the temperature of the liquid increases, the gas becomes less soluble. If a wine is stored or served too warm, the dissolved gas can rapidly come out of solution upon opening, increasing the perceived level of fizziness. This effect is purely physical and can make an otherwise stable wine appear bubbly. Cold storage increases the solubility of the gas, helping to keep it integrated into the liquid until the bottle is opened.
To determine if the wine is merely fizzy or truly spoiled, consumers should look for signs beyond the bubbles. Severe cloudiness, a thick film on the wine’s surface, or distinctly unpleasant aromas, such as vinegar, rancid butter, or nail polish remover, suggest spoilage bacteria have been active. If the wine only shows light effervescence and the flavor is otherwise acceptable, the wine is likely safe to consume. If the slight fizz is unwanted but the flavor is good, the gas can be easily released by vigorously swirling the wine in the glass or pouring it into a decanter.