As of 2015 the new International Grading Standard has been adopted.  The four new grades are as follows:

Grade A Golden  – Delicate Maple Taste
—Grade A Amber – Rich Maple Taste
—Grade A Dark – Robust Maple Taste
—Grade A Very Dark – Strong Maple Taste

These grades have specific and important upper and lower limits for color and flavor. As a rule, the darker the color, the stronger the maple flavor.

What causes the different grades is the sugar content in the sap and how long it’s boiled.  With low sugar content in the sap, it requires more time to get it condensed into syrup.  This allows the sugar more time to caramelize giving it a darker color and a deeper flavor.  There is no difference in sugar content or thickness between the different grades of syrup.

A comparison of the new vs. old grading system is shown below.  You can see the new grade called “Amber” is actually a combination of the old grades “Medium” and “Dark”.  And the new “Dark” is a combination of the old grades “Dark” and “Grade B”.