What is a distinguishing feature of Reserva Ruby Port?

Reserva Ruby Port is characterized by its additional aging requirements, which set it apart from standard Ruby Port. The production of Reserva Ruby involves a minimum aging period in oak casks, typically three to five years, allowing the wine to develop more complex flavors and a greater depth of character. This aging process provides a smoother texture and enhances the wine's overall quality.

In contrast, standard Ruby Port is generally not subjected to the same aging requirements and is designed to be enjoyed at a younger age, typically showcasing more primary fruit flavors and a fresher profile. This distinction in aging is what elevates Reserva Ruby to a higher status within the classification of Port wines.

The other options do not accurately describe Reserva Ruby Port: it is not sweeter than standard Ruby Port, which can vary in sweetness; it is not made exclusively from white grapes, as Ruby Port is typically produced from red grape varieties; and it is not primarily fermented in stainless steel, as fermentation for Port wines often occurs in open fermenters or traditional lagars, allowing for enhanced extraction of color and flavor from the grape skins.