What is Oloroso Sherry cask?

Oloroso is a Spanish sherry that is distinctively dark, rich, full-bodied, and nutty, often containing complex and wide-ranging notes, which is why casks used to age it are prized by producers of whisky, rum, and now Patrón tequila.

Patrón Sherry Cask Aged Añejo is fully matured in casks formerly used to age Oloroso Sherry—the only wood the liquid has ever known. As a result, the interaction helps the tequila evolve into an even more nuanced, buttery expression with rich notes of dried fruit, caramel, vanilla, clove, pecans, and walnuts. Underneath all of that, though, it has still retained the unmistakably peppery, herbal-citrus, sweet agave and mildly vegetal character that’s at the heart of all tequilas from Hacienda Patrón.

What is Oloroso Sherry cask?