Solera aging is an process of aging wine or spirits to create a more consistent product over a long period of time.
Typical 3 year Solera system: Oak barrels in three vertical tiers are filled with whiskey. After one year, 25%-50% of the contents of the bottom barrels are removed, bottled and replaced with aged whiskey from the barrels above, which are then topped off with the contents of the top barrels. New whiskey is added only to the top barrels. This cascading continues and only the oldest whiskey from the bottom barrels, or Solera, is bottled.