Añejo ("old") Tequila is aged in wooden barrels (usually old Bourbon barrels) for a minimum of 12 months. The best-quality anejos are aged 18 months to three years for mixtos, and up to four years for 100% agaves. Aging Tequila for more than four years is a matter of controversy. Most Tequila producers oppose doing so because they feel that "excessive" oak aging will overwhelm the distinctive earthy and vegetal agave flavor notes.