Solera is the traditional Spanish method of blending fortified wines with the intent of smoothing out the differences between vintage years and improving the quality of the wine as a whole. Barrels of older wines are topped with slightly younger wine (from barrels stacked directly on top), which both refreshes the older wine and adds character, body, and depth to the younger wine. The labor-intensive solera system is most famous in the Jerez region of Spain for sherry production, but is used in other regions as well.