Oloroso sherry casks are barrels used to age a specific type of fortified wine known as Oloroso sherry. This sherry is produced in the Jerez region of Spain and is characterized by its rich, nutty flavors and dark color. The casks are typically made from American or European oak, which contributes to the wine's complexity and depth. These casks are often repurposed for aging spirits, such as whiskey or rum, imparting unique flavors to the final product. The residual characteristics of Oloroso sherry, including notes of dried fruit, spices, and chocolate, enhance the profile of the spirits aged in these barrels.