How Long Does Unopened Rum Last? Unopened bottles of rum — including our delicious Slydog Spiced Rum — can last for years (even decades). Thanks to the high alcohol content (around 40%), bacteria or mould don’t grow in it.As long as the bottle is sealed tight and stored away from heat and sunlight, it’ll stay perfectly drinkable. Does Opened Rum Go Bad? Here’s where it gets interesting. Once you open your bottle, air starts interacting with the rum, slowly changing the flavour over time.While your spiced rum won’t “spoil” like milk would, after about 1–2 years the flavour can start...