Maker's Mark bourbon bottles
How To Tell If Bourbon Has Gone Bad
To tell if your bourbon has gone bad, first check the color. If the color has faded significantly, it's a sign the bourbon is no longer at its peak, usually due to light exposure.
Next, make sure it doesn't smell moldy or sour. Finally, if the flavor is weak or unpleasant in a way you don't expect, the bourbon is past its prime, likely due to oxygen or heat.
A sealed bottle is unlikely to spoil and can go for years or even decades without a detectable change in quality, but once opened, it's exposed to air and begins to oxidize.
This chemical reaction slowly but surely alters its taste, smell, and appearance, and you'll only have eight months or less to enjoy the bottle before it begins to noticeably turn.
To slow down spoilage, store the bottle away from excessive heat and light. It's best to store bottles upright to prevent cork decay and reduce contact with oxygen.