You can get maple syrup in different grades, but what defines the difference between the grades? Why is one syrup grade A and one grade B?
The grades of Maple syrup indicate depth of flavor and amount of light transmittance. Grade A is the lighter with Grade B being darker. The letters are just a means of indicating variance of flavor/color, not a judge of quality. Lighter grades are usually used on pancakes, waffles, etc. while Grade B is best as an ingredient in cooking/baking due to the deeper flavor. I prefer Grade B myself but it is generally not widely available outside of New England without purchasing via mail order. Trader Joe's markets usually carry it however.
Lighter syrups are usually the result of earlier harvested saps and the darker ones are from later harvest. Time of season and changes within the trees is what will determine the color/flavor, not the boiling process.
The grades reflect how much light can get through some standard quantity of maple. The darker maple syrups tend to have a stronger maple flavor and tend to be harvested later in the season. The collected sap needs to be concentrated and purified to make the syrup, which is traditionally done by boiling and skimming off impurities.
The USDA (United States Department of Agriculture) and the CFIA (Canadian Food Inspection Agency) have similar grades for maple syrups:
The CFIA standard requires measuring the grades using green light (560nm) light.
Historically, these grades were established before white cane sugar became inexpensive and common, so the "best" maple syrup was the least strong, or Grade A. Now we seek out that maple flavor on corn flapjacks or waffles, so the "best" maple syrup is Grade B.
I find that the best pancakes are made with 2/3 cornmeal to 1/3 whole wheat or buckwheat flour (or any wheat flour, really) rather than just pancake mix. The cornmeal makes them crisp. And Grade B maple syrup, of course.