Which grape variety is known for retaining acidity during ripening and produces its finest wines in Bucelas DOC?

The grape variety known for retaining acidity during ripening and producing its finest wines in Bucelas DOC is Arinto. This variety is particularly valued for its ability to maintain freshness and vibrancy even in warmer climates, which is essential for creating high-quality white wines. Arinto has a naturally high acidity that contributes to the structure and aging potential of the wines made from it. In Bucelas DOC, located near Lisbon, the climate and terroir together enhance Arinto's characteristics, resulting in aromatic wines that often display citrus and mineral notes alongside crisp acidity.

Chardonnay, while versatile and widely grown, typically does not show the same level of acidity retention as Arinto, particularly in warmer regions. Sauvignon Blanc, known for its pronounced acidity, does not typically dominate in Bucelas DOC, where Arinto is the star. Riesling is celebrated for its balance of sugar and acidity but is not traditionally associated with the Bucelas region. Thus, the distinctive qualities of Arinto make it the correct choice in this context.