Effect of heating on the headspace volatiles of Finnish birch syrup

The volatiles of birch syrup, heated from 0 to 10 min at 100°C, were analyzed by GC, GC-MS, and by an experienced panel of judges. Some aliphatic carbonyl compounds, especially 3-methylbutanal, 2-methylbutanal, and 2,3-pentanedione, as well as dimethyldisulfide increased markedly in the samples upon heating. Heating birch syrup reduced the aroma intensity of vanillin, had little effect on furaneol, and increased development of burnt aromas. The burnt aroma of the heated syrups paralleled the amounts of dimethyldisulfide. Heating samples in open vials generally resulted in less burnt aroma and greater caramel and furaneol aromas. In comparison with maple syrup, birch syrup was distinctly stronger in furaneol, caramel and burnt aromas, and lower in vanillin aroma.