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 and watch its temperature. At 235°F/ 113°C, or about 85% sugar, the cook can stop the concentration process and make fudge; at 270°F/132°C, or 90%, taffy; at 300°F/149°C and above, nearing 100% sugar, brittles and hard candies.