What is the key characteristic of a "passito" wine?

A "passito" wine is characterized by being made from dried grapes, which enhances the natural sweetness of the resulting wine. This process involves harvesting grapes that are typically left to dry for a period of time after picking, concentrating their sugars and flavors. As the grapes lose moisture, the sugars become more concentrated, leading to a sweeter wine once fermentation occurs.

This method is traditional in certain Italian wine regions, and the unique characteristics and richness derived from this drying process contribute significantly to the complexity and taste profile of passito wines. The sweetness and depth of flavor set these wines apart from other styles that utilize freshly harvested grapes. Other aspects, such as aging in oak barrels or organic vineyard practices, may pertain to certain passito wines but do not define the category itself. Therefore, the essence of a passito wine lies in the use of dried grapes, making option B the key characteristic.