What is the primary role of yeasts in the winemaking process?

The primary role of yeasts in the winemaking process is indeed to transform sugar into alcohol and carbon dioxide. When grapes are crushed during the winemaking process, the natural sugars present in the grape juice—primarily glucose and fructose—are converted by yeast through fermentation. This process not only produces alcohol, giving wine its potency, but also carbon dioxide, which is a natural byproduct of fermentation. This transformation is essential for producing wine, as it is the foundation of the winemaking process.

While other options mention important aspects of winemaking, they do not accurately represent the critical function of yeast. For instance, color in wine primarily comes from grape skins and related compounds during maceration rather than yeast activity. Similarly, the enhancement of grape flavor is influenced more by grape variety, terroir, and winemaking techniques rather than the yeast itself. Lastly, filtering impurities is a process executed in post-fermentation, utilizing different methods rather than relying on the role of yeast in fermentation. Thus, the value of yeast in winemaking fundamentally lies in its ability to convert sugar into alcohol and carbon dioxide.