Old Charter Oak Chinkapin Oak is the fourth limited edition release from Buffalo Trace in its exploration of oak tree varietals. The Kentucky straight bourbon is made with the distillery's mash #1 (corn, rye, malted barley). Harvested from the Midwest US, the Chinkapin oak was made into barrels from staves which air dried for 24 months. Typically, Buffalo Trace chars its barrels for 55 seconds for a number 4 char. These were only charred for 35 seconds for a number 3 char. The bourbon matured for 9 years in these barrels before bottling at 93 proof.