Sweet maple
All maple syrup sold under the name "pure maple syrup" is only that, maple syrup and nothing else. Otherwise it's illegal to call it that. Maple sap is 2 to 4 % sugar, syrup is 66%.
Syrup is obtained by concentrating the sap at a ratio of about 40 to 1, depending on the sap's sugar content. To be legal, the concentration must always be the same. It must boil at 209 degrees Farenheit, or read 32.0 degrees Baumé or 59.0 degrees Brix at the boiling point.
The taste (aha!):
Several factors, inlcuding the time of the season, the amount of time the sap has spent unprocessed, and the manufacturing process.
The later (warmer) in the season, the darker the syrup. The bacteria in the sap (destroyed during the transformation process) change the fructose into glucose-sucrose.
Wood evaporation versus oil. Also, some maple "factories" use reverse osmosis machines to reduce evaporation time.
Sap collection method: buckets versus pipeline. Some large operations also use pumps to change the hydrostatic pressure within the tree to extract more sap (would love to see those trees in 20 years...).
I make maple syrup on a limited scale, using buckets for collection and a wood-fired evaporator. 1st batch actually came out today...
Yum!