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Maple syrup contains a wide variety of polyphenols and volatile organic compounds, including vanillin, hydroxybutanone, lignans, propionaldehyde, and numerous organic acids. It is not yet known exactly all compounds responsible for the distinctive flavour of maple syrup, although primary flavour-contributing compounds are maple furanone (5-ethyl-3-hydroxy-4-methyl-2(5H)-furanone), strawberry furanone, and maltol. New compounds have been identified in maple syrup, one of which is quebecol, a natural phenolic compound created when the maple sap is boiled to create syrup. Its sweetness derives from a high content of sucrose (99% of total sugars). Its brown colour – a significant factor in the appeal and quality grading of maple syrup – develops during thermal evaporation.