Maple Syrup

Unopened maple syrup keeps essentially indefinitely in the pantry. Once opened, it must be refrigerated, where it keeps about a year.

This is the point people miss most often. Real maple syrup is not shelf-stable after opening — it will grow mold on a counter within weeks. Pancake syrup made from corn syrup will not, which is where the confusion comes from.

Store it in a glass container if you decant it; syrup keeps better in glass than plastic.

For very long storage, maple syrup freezes without solidifying fully because of its sugar concentration — it stays pourable and keeps for years.

If mold does appear, discard the syrup. Older advice about boiling and skimming is no longer recommended.

Maple syrup is around 66% sugar, and that concentration is what preserves it. Sugar binds water, lowering the water activity to a level at which bacteria cannot grow — the same principle that preserves jam and honey.

But maple syrup sits closer to the edge than either. At roughly 33% water it has enough available moisture for molds and osmophilic yeasts to establish themselves once the sterile seal is broken and airborne spores get in. Refrigeration is what slows them, and it is genuinely necessary rather than precautionary.

Pancake syrup is a different product entirely — corn syrup, water, caramel color, and flavoring, with preservatives such as sodium benzoate, and typically no maple at all. It is formulated to be shelf-stable after opening, which is why the two behave so differently and why the bottle instructions differ.

If mold grows on maple syrup, current guidance is to discard it. Older cookbooks recommended skimming the mold and reboiling, but because mold filaments and possible mycotoxins extend into the liquid below the visible growth, that is no longer advised.

Crystallization at the bottom of a jar is sugar coming out of solution — harmless, and it redissolves with gentle warming. Darkening over time is normal. A fermented or alcoholic smell means yeast has taken hold and the syrup should go.