What happens to the bubbles in sparkling wine during secondary fermentation?

During secondary fermentation in the production of sparkling wine, yeast converts sugar into alcohol, producing carbon dioxide gas as a byproduct. This carbon dioxide gas becomes trapped in the liquid, leading to the formation of bubbles. The pressure that builds up in the sealed fermentation vessel keeps the carbon dioxide dissolved in the wine, creating that characteristic effervescence. As a result, when the wine is eventually opened, the pressure is released, allowing the carbon dioxide to escape and form bubbles. This process is essential for developing the sparkling quality of the wine and leads to the characteristic "fizz" that consumers enjoy. Therefore, the correct answer reflects the core mechanism of how carbonation is developed within sparkling wine during secondary fermentation.