Maple sap runs best when daytime temperatures are in the high 30s to mid-40s and overnight temperatures are below freezing. This cycle of above-freezing days and below-freezing nights needs to continue for several days, although nature occasionally has been known to provide a good run under less perfect conditions.
Sometimes sap flows as early as January or as late as May, but in Minnesota, sap usually runs from about March 15 to April 20.
How does the sap turn into syrup?
Sap is converted to syrup by boiling. Most of the water boils out of the sap, leaving behind the sugar and the flavor. It usually takes 30-40 gallons of sugar maple sap to produce one gallon of pure maple syrup.