Jefferson’s Ocean Aged At Sea Bourbon is matured in American oak casks for approximately seven to eight years on land, before the casks are placed on a ship and allowed to rest for another five to ten months at sea. At sea, the bourbon and oak casks are forced to mingle with each other as the ship rolls back and forth over the water. In addition, the temperature and barometric pressure fluctuations during the sea voyage cause the oak staves to expand and contract, and allow the bourbon to extract more of the tannins and flavor from the oak during its maturation.