Which type of wine is characterized by its fermentation process that traps carbon dioxide?

The correct choice is sparkling wine, which is uniquely characterized by its fermentation process that captures carbon dioxide, resulting in bubbles. This is achieved through a secondary fermentation that typically occurs either in the bottle, as in the traditional method (or méthode champenoise), or in large tanks, as in the Charmat method. The trapped carbon dioxide is what gives sparkling wine its characteristic effervescence.

Still wine, in contrast, is fermented in such a way that all carbon dioxide is allowed to escape, leading to a flat finish without bubbles. Sweet wine refers to wines that have higher residual sugars but does not inherently involve the trapping of carbon dioxide. Fortified wine has additional alcohol added, typically through the addition of spirits, resulting in a different profile than that of sparkling wines and does not involve a fermentation process that leads to bubbles.

Thus, the defining feature of sparkling wine, which is the intentional capture of carbon dioxide during fermentation, sets it apart from these other categories.