Solera – a stack of barrels where a small portion of whiskey is removed periodically and new whiskey is added. No barrel is ever fully emptied, and age and complexity gradually increase over time. Hillrock marries small barrel-aged Hillrock Estate Bourbon with mature seed bourbon before finishing in 20 year-old Oloroso Sherry casks to balance the flavors and add layers of complexity Current average age of the Hillrock Solera Bourbon is over 6 years and the rye content is approximately 37%