Imagine barrels of beer, stacked as far as the eye can see, row upon row of wooden casks tenderly nurturing their contents as they age over years. It’s a lovely image, isn’t it? Now imagine that–every once in a while–your friendly neighborhood brewer cracks open the eldest barrels of their generation, drains portions of their liquid bounties, and then tops them off with beer from the adolescents of the bunch. The drained beer is bottled. The elder barrels get a shot of youthful vigor in the arm. The adolescent barrels get a top off from the older barrels. The brewer’s thirsty patrons top off their glasses. The circle of barrel-aging beer life continues. Everybody’s happy.