What is the effect of contamination by unwanted microbes during winemaking?

Contamination by unwanted microbes during winemaking can indeed spoil the wine. This spoilage occurs as unwanted microorganisms, such as certain bacteria and wild yeasts, may lead to the production of off-flavors, undesirable aromas, and spoilage compounds. For example, if spoilage bacteria like acetic acid bacteria thrive, they can produce volatile acidity, resulting in a wine that smells and tastes vinegary and unpalatable.

Additionally, unwanted microbes can disrupt the fermentation process, leading to stuck fermentations or the production of undesirable byproducts that compromise the wine's quality. While some microbial activity is beneficial and intentional in fermentation (e.g., using selected yeast strains), contamination by pathogens or spoilage organisms generally results in negative outcomes for the wine, thereby underscoring the importance of maintaining high sanitation and fermentation practices in the winemaking process.