Cooking the Syrup Raises the Sugar Concentration As a sugar solution boils, water molecules evaporate from the liquid phase into the air, while the sugar molecules stay behind. The sugar molecules therefore account for a larger and larger proportion of all the molecules in the solution. So as it boils, the syrup gets more and more concentrated: and this in turn causes its boiling point to continue to rise. In order to make a syrup of a given sugar concentration, all the candy maker has to do is heat a mixture of sugar and water until it boils, and then keep it at the boil