As long as it is sealed and maintained at the ambient temperature, a can of maple syrup can be preserved during a long period of time, as long as several years. However, once opened, it is strongly recommended to transfer the maple syrup into a plastic or glass container and to refrigerate it to slow down the evaporation process. For long periods of preservation, keeping maple syrup into a freezer is the ideal option.
At 66 degrees Brix, maple syrup is saturated in sugar, and while its water evaporates, its sugar density increases. In fact, as soon as a can of maple syrup is opened, the evaporation process is triggered automatically, thus increasing the syrup’s sugar concentration and resulting in crystallization of the excess sugar.
Light-coloured syrup harvested in early season is particularly susceptible to crystallize because of its high concentration of saccharose. However, slightly darker syrup contains more fructose and has a lesser tendency to crystallize. Saccharose is more sensitive to variations in degrees Brix.
A glass bottle of maple syrup can be kept at room temperature. It can be preserved in the same conditions as a can of maple syrup. However, it is not recommended to expose the bottle to light. Yet it is not advised to keep it in the freezer.
As long as the can of maple syrup is sealed hermetically and maintained at proper temperature, it is not necessary to freeze it. In the refrigerator, the product can be kept for a few months (from three to six months). For long periods of preservation (of at least one year), keeping maple syrup in a freezer is the ideal option.
* The degree Brix is the weight in grams of dry matter contained in 100 grams of solution in distilled water (measure relative to maple syrup density
Source : Federation of Quebec Maple Syrup Producers