A bottle of maple syrup can be expensive—especially if you're buying that Grade A, totally pure stuff—so there's no shame in wanting to know how long syrup lasts. After all, you want to be able to use that maple syrup for as long as possible. So does syrup ever go bad? The short answer is technically no, syrup does not expire and you can keep an unopened container of the stuff on your shelf indefinitely. That's due to the high sugar content of pure maple syrup, according to the experts at Ben's Sugar Shack, which produces syrup in New Hampshire. This is actually the same reason why honey never expires; bacteria have a hard time growing in these high-sugar, low-moisture environments.
But one difference between honey and syrup is that syrup can get moldy after the container's been opened, exposing the syrup to air. The good news is that this mold isn't like the mold that ruins fruit; it's a totally different type of fungus that doesn't affect the syrup. In other words, moldy syrup is still safe to eat—but you have to remove the mold first.
The easiest way to remove mold from maple syrup, according to the folks at Epler's Maple Syrup, which makes maple syrup in Pennsylvania, is to skim off the layer of mold on top. Then heat up the remaining syrup to its boiling point to kill the offending spores. Let that cool a bit, skim off any mold that may still be lingering, and reheat it again. Then it's ready to go.
Things are a little bit different if you're buying pancake syrup, not pure maple syrup. Pancake syrup is often a type of corn syrup that's been flavored. Much like maple syrup, pancake syrup doesn't spoil. It's safe to eat for "an indefinite period of time regardless of whether it has been opened," according to Karo, which manufactures both a pancake syrup and several types of corn syrup. You don't have to store pancake syrup in the fridge, though. Room temperature is just fine, but if you're buying the stuff that comes from a tree, be sure to keep it in the fridge to avoid any moldy situations.