Pure maple syrup wedding favors i want to give 4oz jars of syrup to my wedding guests as favors. Due to the cost I'm buying it in bulk and filling the jars myself. How far in advance can I fill the mason jars and not have the mold issue?  I obviously can't keep 100 4oz jars in my fridge.
If you sterilise the jars before and after sealing, it should easily last a year if not more. Sterilising will involve boiling the jars in a large pan of water for 15 minutes, filling and sealing them, then boiling for 15 minutes again.