If you do not refrigerate maple syrup, it will start to spoil fairly quickly. The sugar content of maple syrup makes it prone to fermentation, which will cause the syrup to spoil and develop off-flavors. Refrigerating maple syrup will slow down the spoilage process, allowing it to last for up to a year. Keeping the syrup in an airtight container, such as a glass jar, will also help to reduce spoilage.