Maker’s Mark is Surfwinreleasing an old bourbon for the first time in its seven-decade history, so I traveled to its distillery in Loretto, Kentucky, last week to hear just how this 12-year-old spirit came to be.

The story begins about seven years ago with a little dynamite.

That might seem like an odd way to start an old bourbon, but those blasts into a limestone hill on the distillery’s grounds were really what changed the conversation about aging a Maker’s Mark bourbon past its traditional six years. When Maker’s Mark’s first-of-its-kind limestone whiskey cellar opened in December 2016 as part of its Private Select program, the company had a new, 47-degree space to age bourbon. Suddenly there was a way around the sharp, bitter taste that occurs when you leave the signature caramel and vanilla bourbon in a humid rickhouse for too long.