The unseen threat to wine

Wine, an elixir savored across the globe, embodies tradition, culture, and sophistication. But like all things exquisite, its quality and purity demand careful guardianship. A subtle misstep in its handling can quickly escalate, turning a potential vintage into mere vinegar. At the heart of this transformation lies the acetic bacteria, a microorganism that, when unchecked, can quickly spoil the sensory pleasure of wine.

From Wine to Vinegar: The Two Stages

Wine degradation can be understood in two distinct phases. The first is 'picado acético', a preliminary stage where the ailment only affects the wine's superficial layers. As the problem grows unchecked, it culminates in 'avinagramiento', a stage where the deterioration pervades the entirety of the wine volume. Here, a good wine is no more, replaced instead by what can best be described as decent vinegar.

The culprits behind this transformation are aerobic microorganisms aptly named 'acetobacter' or acetic bacteria. These bacteria oxidize ethanol in the presence of oxygen, converting it into acetic acid through a chemical reaction. Simply put, when alcohol, oxygen, and acetic bacteria combine, the result is acetic acid, synonymous with spoiled wine. This spoilage can manifest at various stages, be it during fermentation or even after bottling. If detected too late, rectification becomes an insurmountable challenge.

Guarding Against Acetic Bacteria

The challenge with acetic spoilage lies not in its cure but in its prevention. Measures include:

• Minimizing prolonged and unmonitored exposure of wine to oxygen.
• Ensuring wine containers, whether tanks or barrels, are filled completely, leaving no air gaps.
• Regulating temperatures, ideally not exceeding 14-15°C, to hinder acetic bacteria proliferation.
• Maintaining optimal levels of sulfurous agents.
• Upholding impeccable hygiene standards across the winery, including tools and apparatus not in direct contact with the wine.

Should corrective measures be necessitated, they're limited to the disease's early detection phase. Techniques such as pasteurization, blending with healthy wines, or even inducing re-fermentation might be employed. But the sobering reality remains: the wine will never regain its original quality.

The Bacterial Assault: Before and After Fermentation

Acetobacter's relationship with wine can be dissected into two phases: pre and post-alcoholic fermentation. Before fermentation, these bacteria ubiquitously inhabit vineyards. Any damage to the grape skin, whether due to adverse weather conditions like hail, pests, or careless handling during harvest, offers an entry point. Hence, the emphasis on short harvest durations and gentle grape handling, often witnessed in high-quality vintages using small baskets.

Post-fermentation, the scenario changes. With alcohol now present, the bacterial activity shifts from proliferation to an outright attack. Oxygen vigilance and maintaining appropriate wine levels in containers become paramount. Wines with an alcohol concentration below 13% are particularly vulnerable.

Organoleptic Alterations: The Acetic Aftermath

When acetic bacteria have had their way with wine, the sensory changes are palpable:

• Visual: The wine's clarity diminishes, sometimes exhibiting a filmy layer atop.
• Olfactory: Aromas reminiscent of rotten apples, walnut, and adhesive emerge, attributed to acetaldehyde and ethyl acetate.
• Taste: The palate discerns heightened sourness and roughness, the handiwork of ethyl acetate and acetic acid.